Tuesday, February 27, 2007

Crunch time

In less than 19 hours I will begin taking an exam. It is worth 70% of the grade of my most important class this semester. It will be the first school exam I have taken in nearly 2 years. It is three hours long. It is the first exam I will have ever taken in Hebrew, though I got (grudging) permission to write the answers in English. The material is all stuff I was totally lost on all semester, and for the most part learned in the last couple weeks, much of it in the last 36 hours, and an undetermined part which I have yet to learn. But my brain is fried and I don't think any of what I'm learning now is being remembered. And even now, just sitting at my desk reading lecture notes, I'm so nervous that my hands are shaking and I can't write a complete sentence. Which is a state I have rarely been in in my life, even during an exam.

My roommate recommended that instead of studying the material, I study Sefer Tehillim.

AAAAAAAAAAAAAAAAAAAAAAAAHHHHHHHHHHH!!!!!!!!!!!!!!!!!!!!!

Hopefully this post will be... I'm not sure what. But I can always hope.

Saturday, February 24, 2007

Small disappointment

I used the abbreviation "fJ" for "femtojoule" in my circuits project report. I was wondering if my usage of such bizarre obscure units would impress the grader, and for that matter anyone else reading the report. But upon searching Google it became clear that in some circles, this is considered a familiar, unremarkable unit. Oh well.

Such is the life of students in my university around exam period. (But not necessarily the rest of the year)

Wednesday, February 21, 2007

What's in a name?

Think of the major Jewish male heroes from Tanach: Avraham, Yitzchak, Yaakov, Yosef, Moshe, Aharon, David, Shlomo. All of them would be great people to name your son after, and in fact these are many of the most popular names given today. And not only today; these names have been popular for something like the last thousand years, from "Moshe Maimonides" and "Yosef Karo" on down.

Perhaps surprisingly, though, the trend does not continue with earlier generations. The great rabbis of the geonic period had names like Amram, Hai, and Saadiah. Not only are these names not familiar from Tanach, it is questionable whether they are even in Hebrew. In the Gemara the situation is similar. The predominant names - like Abayei, Zeira, Pappa, and Assi - are foreign sounding and definitely not from Tanach. The Mishna, at least, is full of Hebrew names such as Hillel, Meir, and Gamliel. But here, too, few of the names represent famous Biblical figures. When Rabbi Yishmael's parents named him, couldn't they have chosen one of Yishmael's more illustrious family members instead? When Rabbi Akiva was born, why didn't they move the yud and take off the alef and just call him Yaakov? (Few female names are recorded from these time periods, so it's hard to tell if they were similarly unorthodox.)

It's interesting to see that the pattern continues even within Tanach. But first, we need to clear up the misconception that every Biblical baby had a name invented for him at birth. In fact, many biblical names are used over and over again. According to a concordance I looked at, there are 10 Michaels in Tanach (not counting the angel), 12 Azaryahus, 4 Yirmiyahus, 3 Ezras, and 14 people named Shallum. There are 8 people named Shlomit, and what's more, 6 of them are male. Repetition of names seems to be the rule and not the exception. It is thus quite striking that all of the really famous names are "exceptions".

So in summary: throughout all of Jewish history until, oh, about the time of Rashi, the names of the most famous Biblical figures were not used. But soon afterwards these names became dominant. Why?

It seems that it was considered presumptuous to use a name which had previously been used by such a great historical figure. To draw a parallel, we name our kids Moshe today, but we probably wouldn't look kindly at someone who actually named their kid "Moshe Rabbeinu". In the olden days, the name Moshe alone had similarly specific connotations. And so for a long time, it wasn't considered acceptable to use that or other similarly famous names.

But at some point in the middle ages, the Europeans came up with a brilliant invention: last names. This invention roughly coincides with a wave of rabbis named Avraham and Moshe, and I suspect it's no coincidence. Once you were referred to by two names, there was no danger that you would be confused with the prophet or king of the same first name. And thus a series of Biblical names with very positive connotations became available for general use. If this has led to the demise of such traditional Jewish names as Rafram and Hai, well, that's just the price we have to pay for progress.

Tuesday, February 20, 2007

I'm legal again

Nearly four months after returning from my last trip to the US, I finally received a student visa today, and am no longer illegally in Israel. I was a just slightly afraid that they'd notice the stamp from the airport, realize that I'd overstayed my visa, and call the police and deport me. Most likely, it was the 300-shekel bribe processing fee that saved me.

By the way, all this happened in the coolest building in Haifa.

Sunday, February 18, 2007

Esther and Batsheva III

Having written last year about the similarities between Esther and Batsheva, I was a little surprised to open the book Hadassah Hi Esther for the first time, and see that the very first article was entitled "Between Esther and Batsheva", and dealt with the similarities between the two. I was much more surprised to find that my list of similarities and R' Bazak's had absolutely nothing in common. I focused on the Uriyah episode; R' Bazak wrote about how Batsheva thwarted Adoniyahu's claim to kingship. While R' Bazak's article is by far the stronger and better argued, I think that the parallels we each found can be combined, thus strengthening both of our arguments. And there may be room for a grand unified theory identifying a common source for the similarities. If I survive the final exams which are coming up soon (and which will probably restrict my blogging output for a while), then maybe I'll find something to say on the matter.

UPDATE: Here is the "grand unified theory" I was looking for.

Saturday, February 17, 2007

Thoughts vaguely related to parshat Terumah

If you want to understand this week's parsha (and next week's), look here. Meanwhile, let me indulge myself by posting a fuzzy-wuzzy dvar torah. But not too fuzzy-wuzzy, it is Gush-influenced after all.

There are two different kinds of lights in the world. Some lights are utilitarian, which guide you and let you do things which are impossible to do in the dark. Other lights have no practical value, but are beautiful or noteworthy and thus are worth looking at in their own right. The obvious natural examples of the two kinds of lights are the sun and the (other) stars. There is no point in looking at the sun (and in fact it's difficult and dangerous to do so), but the sun's light allows us to do things during the day. Meanwhile, the stars don't provide too much light, but they are certainly worth looking at.

Halacha includes examples of both kinds of lights. Shabbat and Chanukah candles are especially good examples. Shabbat candles are utilitarian; their point is to provide "shalom bayit" by making the house brighter and more fun to be in, and for this reason some authorities say they should be placed in every room of the house. Meanwhile, Chanukah candles by definition have no utilitarian use. After lighting them we say "we have no permission to use them, but only to look at them" and we add a "shamash" candle in case we accidentally do use their light. The only thing we do with Chanukah candles is watch them. Upon seeing the eight candles we are reminded of the eight days of the miracle, and thus the purpose of the candles is fulfilled.

In this week's parsha we read about another halachically required light: the menorah in the Temple. Is this light meant for illumination, or is it meant to be looked at? It turns out that the answer is both. One candle was supposed to be lit "constantly" to serve as a continuous indicator of the relationship between Israel and God. Meanwhile, the menorah as a whole was the only source of light within the Temple. Thus the menorah is both a source of light and a symbol to be looked at.

Finally, the Torah itself is compared in Jewish tradition to light. As with the menorah, it seems that both kinds of light are intended in the comparison. Torah study is of course necessary if you want to find out the halacha. In this sense, the Torah is a useful tool which illuminates and guides our search for halachic decisions and moral standards. At the same time, Torah study is worthwhile even without these practical results. It is an opportunity to encounter God, a potentially prophetic experience by which God speaks to you through the texts. It can and should be desired "lishmah" - independent of its practical value.

Hopefully while studying Torah, and for that matter in our religious life as a whole, we can take advantage of both aspects of the "light": using the Torah creatively and precisely to achieve positive results, while at the same time appreciating and seeking an intimate understanding of it and an intimate relationship with its Giver.

(Derived from a dvar torah by Menachem Lazar, Chanukah 5766)

Thursday, February 15, 2007

Connotations

Would you be alarmed to learn that your "bus driver" was "bipolar"? Not if you'd taken a VLSI course with me.

A heftza from the gavra

A large number of downloadable shiurim given by R' Soloveitchik, in English. Now, I just have to find time to listen to them.

I had to come here, in order to write this

"The air of Eretz Yisrael makes one wise" (Bava Batra 158b)

This phrase has undoubtedly been explained in many ways; I now want to look at R' Kook's interpretation in Orot Hatorah (beginning of chapter 13, "Torat chutz laaretz vetorah eretz yisrael"). R' Kook relates the difference in wisdom to the difference between the revealed ("nigleh") and the hidden/mystical ("nistar") Torah. Specifically, when learning Torah outside Israel, one is able to access the wisdom of the hidden Torah while learning "aggadah" (nonlegal material) but not while learning "halacha". Meanwhile, in Israel one can draw on the hidden Torah while learning both "aggadah" and "halacha".

This interpretation is surprising because it implies that one can access the hidden Torah, without being a kabbalist or whatever, simply by learning Torah in the normal manner by which Torah is learned. It is also problematic because it seems to contradict the principle of "lo bashamayim hi" - that halacha is decided based solely on analysis of the relevant sources, ignoring appeals to authority or to special divine revelation.

For these two reasons I suspect R' Kook is not talking about "hidden" and "revealed" Torah as is generally meant. I would instead interpret R' Kook by noting that people are not 100% rational, that due to differences in background or psychology it is possible for intelligent people to arrive at different answers to the same question. This is probably the meaning of the expression "seventy faces of Torah", that numerous different interpretations of Torah can all be correct - because interpretation necessarily depends to some extent on who is doing the interpreting.

I wonder if this unquantifiable variation in our thinking is what R' Kook calls the "nistar" or hidden Torah, while the "revealed" Torah consists of those logical processes and conclusions which are objective and independently verifiable. When learning "aggadah", which is subjective and personal, each person's unique personality and thought processes are inevitably involved. Thus, someone learning "aggadah" always has access to "hidden" Torah. For "halacha", though, the story is different. Halacha is supposed to be absolutely rational and objective. But no human being can meet this standard, so halachic analysis must necessarily include some subjectiveness. The question is which subjective elements enter the analysis, and where these elements come from.

There are a number of different possible sources for subjectivity. Your childhood education or innate personality characteristics, for example, could potentially and unavoidably bias you in one way or another. But it seems clear that halacha is "agnostic" towards these factors. Though these factors might influence two people to give slightly different answers to the same halachic question, both answers would be fully acceptable and both would fall within the rubric of "seventy faces to Torah".

But there is at least one factor for which halacha DOES "choose" one subjective inclination over another. Regarding the influence caused by physical location, the "correct" bias is by definition that of person in Israel. To the extent that your thinking is subtly affected by the geography, social/political structure, and historical associations of the place you live in, inhabitants of Israel are at an advantage in determining the correct halacha. Not only for halachot which apply only in Israel, but also for halachot which are universal.

Now, this does not mean that halacha is determined solely by Israelis. The "hidden" subjective Torah is only one factor in the halachic process, and may often be less important that the "revealed" logical understanding of the law. If a person outside Israel has the sharpest mind, most likely halacha will be decided like him, though he cannot take advantage of "hidden" Torah. But all things being equal, a person's halachic analysis will be most accurate in Israel. There he will be able to draw on the subjective "hidden" Torah as well as the objective "revealed" Torah as part of the halachic process.

As always, our goal is to "know God in all [our] ways" (Mishlei 3:6). It may be that only in Israel can this be fully accomplished.

Wednesday, February 14, 2007

Truly out of this world

Aurora borealis on Saturn

YES!!!!!

Now, if they will only enforce this consistently, to let all Haifa dog owners know that's not OK to poop on my sidewalk. I can hope...

Monday, February 12, 2007

Thoughts on Mishpatim

Now these are the laws which you shall set before them:
If you buy a Hebrew slave, six years he shall serve; and in the seventh he shall go free for nothing.
(21:1-2)

It's interesting that the legal code begins with slavery. Obviously this was a touchy subject among the Israelites who were freed from slavery only weeks earlier, and perhaps they were uneasy and waiting to see exactly what form slavery would take under the newly issued legal code. As it turns out, the period of slavery is limited to six years, and the slave's family may not be disrupted. Both of these conditions, of course, are in contrast to the Egyptian slavery, which was apparently unending (Haggadah: "If God had not taken us out of Egypt, we'd still be slaves today") and involved babies being thrown into the Nile. Later on in Mishpatim, there are other laws relating to slavery. But perhaps these laws at the beginning are the ones the Israelites were especially anxious about and looking forward to.

If a man strikes his male or female slave with a rod, and he dies under his hand, he shall be avenged.
But if he survives a day or two, he shall not be avenged; for he is his money.
(21:20-21)

It's hard to argue that if the slave survives for a couple days, then the owner is off the hook entirely. After all, seven verses later we read that a slave whose tooth is knocked out goes free. If the slave is killed, by the same logic the slave should AT THE VERY LEAST go free. And there's not even much satisfaction in the technicality that a dead slave cannot go free.

Notice that the passage twice uses an unusual word - "avenged". In ancient societies with weak central justice systems, the best way of deterring murder was to allow the victim's family to avenge the killing. The Torah preserved this system, though limiting it to the period before the killer could flee to a city of refuge or be put on trial. The presence of the word "avenged" here indicates that we are not talking about normal punishments, but solely about vengeance by the slave's family members.

It seem that if a slave were to be beaten to death, the slave's relatives could kill the master, just as in any normal case of manslaughter. This despite the master's excuse that he clearly did not intend to kill his own property. But if the slave survived a little while before dying, there would be an additional element of uncertainty. Perhaps the master's beating was not of a severity that could be expected to kill the slave, or perhaps the slave in fact died from some other cause. In this situation, because there are additional mitigating factors to the master's deed, the option of vengeance is not available.

In addition to the possibility of vengeance, it is not stated what judicial punishment you would incur by beating a slave to death. But the other laws in Mishpatim strongly hint that such a punishment did exist.

Eye for eye, tooth for tooth, hand for hand, foot for foot. (21:24)

The simple meaning of this verse seems to indicate corporal punishment, while modern-day halacha says that monetary compensation is required instead. These two interpretations must be reconciled with each other, as well as with our sense of morality.

At least one source in Chazal (Pesikta Zutrati-Lekach Tov on this verse) states that at one point in the past, corporal punishment was in fact practiced by Jews, according to the simple meaning of the verse. R' Yerucham Fishel Perle (in his commentary to R' Saadiah Gaon's List of Mitzvot, 3:29) has a brilliant interpretation of this which, in my mind, solves all problems. According to him, the basic law always required corporal punishment, but it was also acceptable to substitute ransom money for the corporal punishment. The Torah prohibits taking a ransom in place of the death penalty for murder (Bamidbar 35:31). But there is apparently no such prohibition regarding ransom for other bodily punishments. Once corporal punishment was deemed fully expendable (in the rabbinic period at latest, long before other cultures regarded corporal punishment as immoral), ransom money became the requirement instead of an option, and thus monetary compensation became the halacha we have today.

UPDATE: the "literally corporal punishment" opinion also appears in the Gemara (Bava Kama 84a), where it is explained away as, basically, not literally meaning what it says. But in P.Z.L.T. there is no explaining away, and the logic behind the ruling is provided, so it is really really difficult to say it is not meant literally.

(Not my bekiut, but that of R' Amnon Bazak and the "Shabbaton" parsha sheet staff :-) )

Sunday, February 11, 2007

Hadran alach siporei hatanach

One of my projects for the past year-plus has been to summarize all of Tanach. I started with Sefer Shmuel, did the rest of neviim rishonim bit by bit, and then moved to the Torah. Earlier today I solved the difficulty I was having with Devarim chapter 31. Shortly thereafter, I finally finished my summary of all the narrative portions of Tanach.

Since the parshiyah breaks are usually the best (and most authentically Jewish) indicators of Biblical structure, I chose them to structure the summary. My goal was to condense each parshiyah into one line of summary. This resulted in a dense but clear summary of the entire book, which I could then analyze for overall structure.

This methodology, derived from what R' Menachem Leibtag likes to do in shiur, had the following long-term benefits:

1. Reference - makes it quick to find anything in the book by scanning your summary
2. Gives a broad overview of the book's meaning - otherwise unavailable without intense study of certain commentators
3. Provides context when you want to study a small part of the book
4. Makes you learn the entire book reasonably well as you are summarizing it. (Much more efficient than by "normally" learning the book.)

I recommend this method to anyone with a laptop, who wants to learn Tanach without spending a year in yeshiva. Go to Mechon Mamre and download the book of your choice as one file. Use the English file, it will make things faster and easier (though it's good to have Hebrew for whenever you don't trust the translation). If a textual issue bothers you, try to fix it, but if you can't, make a note and keep going. The point is to gain overall knowledge, not resolve specific textual issues. Periodically, look at what you've written and try to get a broader sense of what is going on in the book. As always, beware that begin and end quotes, if they existed, would not always be where you'd expect.

Because the level of thinking required is not extremely high, this summarizing can be a highly productive use of many hours spent in buses or waiting for appointments or just being too tired to do real work.

I'm posting my summaries for whoever might be interested. It would be nice to post attachments, but Blogger doesn't seem to allow this. So use the following links, and copy and paste the text to a file: Torah Narrative portions of nach

My next task is the rest of Nach - the prophecies and most of Ketuvim. But the format for this will probably have to be different. By summarizing a section of prophecy or psalms in one line, you'd probably lose most of the meaning. So I'll probably have to choose larger chunks of text and write short paragraphs to summarize each of them. Or something like that. Suggestions are welcome.

Saturday, February 10, 2007

Question for a shadchan

If you knew two people with first names David and Batsheva, and they seemed appropriate for each other, would you try to set them up?

Would the "name factor" make you less likely to set them up? Or perhaps more likely?

(The same question can be asked regarding other "notorious" pairings of "normal" names, for example Yehudah/Tamar, Amnon/Tamar, Aviyah/Maacha, add your own here...)

Friday, February 09, 2007

Thoughts on Yitro

Moshe chose able men out of all Israel, and made them heads over the people: authorities over thousands, authorities over hundreds, authorities over fifties, and authorities over tens. They judged the people at all times; the hard cases they brought to Moshe, but every minor case they judged themselves.
Moses let [Yitro] depart, and he went to his own land.
(18:25-27)

These lines are chronologically problematic for two reasons. 1) Moshe retells the story of the judge selection in Devarim 1, but there it seems that selection of judges came after the giving of the Torah, whereas here it is told before the giving of the Torah. 2) "Yitro" seems to go home immediately after this story, but according to Bamidbar 10:29-30 "Hovav" stayed with the Jews until long after the giving of the Torah. And there is reason to think that Yitro and Hovav were the same person (even if you're normally skeptical of midrashic name-equations).

I would add a third question. Why exactly do we need to know that Yitro went home? What does this line add to the story?

We can understand these verses by looking back to last week's parsha. There, the Torah tells us about the manna which began falling and kept the Jews alive in the desert. At the end of the story (16:35), we read that "the descendants of Israel ate the manna for 40 years, until coming to a settled land". This line could not have been written until the end of the 40 years, and thus chronologically it belongs at the very end of the Torah. But we accept it here, without a second thought, because it's informative and obviously not meant to be chronological. And it's more logical to put this line here, with the rest of the manna story, than to stick it into some random place in Sefer Devarim.

The same logic applies to the Yitro story. Most of the story takes place within 24 hours of Yitro's arrival. But - and this should be obvious, though for some reason nobody thinks of it - Moshe's choice of judges clearly cannot have taken place that same day. Moshe had to choose judges over "thousands... hundreds... fifties... and tens" of people, for a total population of at least 600,000. It would be impossible to appoint all these thousands of judges in one day. Like the 40 years mentioned in last week's parsha, the period of picking judges actually took a long time, and is only mentioned here to "finish off" the topic even though its chronological conclusion was much later.

With this understanding, the final line of the story makes much more sense. The chronological problem is solved, since Yitro only left after all the judges were chosen, which could easily have been a full year later when Hovav is recorded as leaving. (If Yitro and Hovav are different people, of course, there never was a chronological problem.) And the question of why we learn about Yitro's leaving can be answered as well. Apparently Yitro would have been willing to leave the day after he had come. But since he had come up with the idea of judges in the first place, he stuck around as an advisor until the plan was successfully implemented. From the fact that Yitro postponed his departure until all the judges were chosen, we learn that he was not only smart enough to make useful suggestions, but dedicated enough to put in effort and make sure that they were actually carried out.

(Partial source... not from Gush for once)

Sunday, February 04, 2007

Super bowl psak

If this isn't urgent, then what is?

Google understands Ashkenaziss

When you search Google for the word "Shabbat", it also finds pages which don't include "Shabbat" but do include "Shabbos".

See for example the following search.

Pretty cool, and I wonder how many other examples of this exist. And if this is hand-coded or if there's an algorithm to find search terms that are determined by users to have the same meaning.

Friday, February 02, 2007

Make it an actual Championship Series

As a St. Louis Cardinals fan I am no doubt happy about last year's the World Series championship. But it feels weird, because the Cardinals were clearly a worse team than in the previous few years, when they didn't win the World Series. There is a feeling (no doubt familiar to NHL fans) that the regular season does not sufficiently count, and the championship is determined by the randomness of a few playoff games and not by who is really the better team. This time, of course, my team took advantage of the system. But that's not something to celebrate, since the clear flaws in the system diminish the significance of what the Cardinals accomplished.

What is needed is a simple but significant change to the first playoff round. Right now the four playoff teams in each league are assigned to play each other essentially randomly. Thus - another flaw with the current system - there is effectively no competition between teams which know they will likely be in the playoffs. I propose, first of all, that the team with the best record of the playoff teams play the team with the worse record (seed 1 versus seed 4), while teams with the 2nd and 3rd best records play each other. Furthermore, I propose that the playoff between teams 1 and 4 go a maximum of 6, not 7, games. Team 1 would start with an automatic "one game advantage", so it only has to win 3 games to win the series, while team 4 has to win 4 games.

Clearly, this would give team 1 a significant advantage over team 4. This in itself would decrease the number of upsets and allow for the better team to consistently advance. Moreover, since team 2 would not have this advantage over team 3, the playoff teams would have strong incentives to compete with each other for the better regular season record. Team 1 would get the one-game advantage which team 2 would not get, and team 4 would get the disadvantage which team 3 would not get. Meanwhile, team 2 would still have the home-field advantage over team 3. So there would be strong incentives for all 4 playoff teams to improve or maintain their position. Instead of the Yankees running away with their division and coasting until the playoffs, they'd have to compete with the Twins or A's or whoever for the important one-game advantage in the playoffs. Thus the regular season would be much more interesting for the top teams.

For reasons of fairness, if there was a tie between teams 1 and 2 or 3 and 4, the one-game advantage would be cancelled. But in all other situations, I think this change would do a good job of making the regular season more interesting, and the playoffs fairer.

Thursday, February 01, 2007

Al tikra pri ela pru (urevu)

On Tu Bishevat we celebrate our connection to the land of Israel. Not many people know that another Jewish holiday lies exactly half a year away from Tu Bishevat. This is Tu Beav, which celebrates our connection to the remainder of the Jewish people. (There's the obvious connection you have with "a certain member" of the Jewish people. But there's also a more specific meaning - Tu Beav is traditionally the date when the entire tribe of Binyamin was once again allowed to marry with the rest of the Jewish people.)

There is a message in the timing of these holidays, exactly six months apart from each other. When you get to the extreme of love for the land of Israel, it is time to turn around and increase your love for the people of Israel, and vice versa. Both are valuable, but ultimately they must accompanied by each other.

(Source)

Crazy day

I was in the supermarket this morning, and some random guy starts talking to me in English. It turns out he's a college student from the US, interning for the semester at a high-tech company. Out of the blue he offers to start a chavruta with me, and of course I agree.

Then when I'm in the checkout line, someone I've met a few times on campus passes by and invites me to a Shabbat meal - which otherwise I might have had to eat by myself. I agree to this too.

Then I go to a meeting with my project advisor. Last time I was so unprepared that he literally told me that "this is not kindergarden" and so I need to start taking my project seriously. But this time I show him all my results, and he has trouble understanding them. When he finally comes up with an explanation, I basically shoot it down. He has to admit that although he thinks he is good at physics, this time the physics doesn't make any sense to him, though it makes perfect sense to me.

Shortly afterwards I'm in my lab running simulations, and an attractive, seriously religious looking girl whom I've never seen before is working two computers away from me (clearly, on a subject very similar to mine). At one point she answer a phone call, mixing her Hebrew with fluent English. Do I find an excuse to get up and start a conversation with her? Well, unfortunately, not this time. But hopefully whatever substance got mixed into my water today will still be there tomorrow or the day after. If so, I'll get to take advantage of the few remaining extraordinary coincidences and opportunities which I didn't take advantage of today.

Special Beshalach/Tu Bishvat edition

[Moshe] cried to Hashem, and Hashem showed him a "tree", and he cast it into the waters, and the waters were sweetened.
There He made for them a statute and an ordinance, and there He proved them, and said: "If you listen carefully to the voice of Hashem your God, and do that which is right in His eyes, and listen to His commandments, and keep all His statutes, I will put none of the diseases upon you which I have put upon Egypt, for I am Hashem who heals you."
(15:25-26)

The word "diseases" is probably a reference to the plagues, though most of the plagues did not seem to directly involve disease. (Although who knows - with all the bugs flying around and the frogs and the bad drinking water, not to mention the plague and the [smallpox?] boils, many of the plagues might have led to sickness of some sort or another.) But why would God need to reassure the people that they would not receive plagues just as the Egyptians did?

In the story to which God's promise is a reaction, the only drinking water available to Bnei Yisrael was salty, and Moshe had to miraculously make it drinkable by throwing in an "tree" ("etz", i.e. some unknown wood thing). This scene bears an striking resemblance to the plague of blood. There too Moshe miraculously changes the water's potability by striking it with a wooden implement (his staff).

Did Bnei Yisrael notice their current lack of drinkable water and associate it with what the Egyptians had gone through in the first plague? Did they perhaps think the 10 plagues were being more or less repeated, now with them as a target? The obvious difference between the two parallel "plagues" is that Moshe made the Nile undrinkable, while now he made the spring drinkable. But assuming the people feared a new set of plagues, Moshe's use of the "tree" would be a carefully chosen gesture, designed to confront the people's fear and show it was unreasonable. Then God would formally promise not to repeat the plagues, and hopefully all irrational fears would be taken care of.

Thus everything works out neatly, except for the obvious question: why on earth would the people fear further plagues in the first place? I can think of two possible reasons. First of all, they had already complained several times to Moshe, and possibly doubted his and God's authority. While this is not yet explicit in the story, we know that not too long will pass before they openly rebel, and even before that it must have been clear where public opinion was headed. Thus, they had reason to expect punishment. Egypt received the plagues because it refused to recognize God's role, and now Israel was denying God's role? Not a good situation.

Alternatively, (some of) the people may have had a woefully unsophisticated theology. In the ancient world it was believed that different natural forces were controlled by different gods, and I'm no expert, but it seems reasonable to assume that some gods were considered "helpful" and others "dangerous" and to be stayed away from. If some of the Israelites thought this way, they might have come to the conclusion that God was a "destructive plague god" whose role was to terrorize whoever was in his midst. So far Egypt had absorbed all the punishment, but with such an out-of-control deity, in whose "territory" the people were now located, it looked like they were the next likely target.

Either way, it would have taken Moshe's demonstration as well as God's promise to convince Bnei Yisrael that by obeying from now on, they could avoid the terrible punishments they had recently seen.

I know this interpretation is interesting; I don't know if it's reasonable.