There are two unique mitzvot on Sukkot - sukkah and lulav. At first glance they seem to have little to do with each other. But it may be possible to discover a connection.
Here is a picture of the top of my neighbor's palm tree.
[BTW: Yes, I do have a stunning view from my apartment window. To those I can't stop mentioning it to, sorry. For more pictures see here.]
Growing out of the top, one can see a single long straight spiky thing. That is the lulav. It seems to me that there is never more than one lulav per palm tree. It first grows as a lulav, and then its leaves fall towards the sides and it becomes a regular palm leaf, at which point a new lulav grows to take its place. We are required to use the leaf in its early lulav stage - if we wait too long it becomes an invalid regular leaf. The lulav looks rugged, but for the purposes of the mitzvah it is very transient.
In this respect, the lulav is similar to at least 2 of the other 3 species. The etrog is a very easily damaged fruit, and the aravah goes dry and falls apart after just a few days after being picked. We see that (at least) 3 of the 4 species share the attributes of fragility and temporariness.
Of course, the sukkah too is fragile and temporary. And it seems this common theme is at the heart of the Sukkot holiday.
The abundant agricultural harvest, which historically happened around Sukkot, poses a theological dilemma. If we ascribe too much importance to our material possessions, it is easy to become proud, callous and corrupt. But on the other hand, it is wrong to become ascetics and deny the significant of the world we live in. There is a tension between these two dangers, and it is resolved by recognizing our prosperity as real, but transient. God has given us prosperity, but God is not guaranteed to do so in the future.
Therefore on Sukkot we celebrate by eating and drinking and singing songs and displaying the fruits we have just harvested. But we do so while living in a temporary home, and using fruits which are chosen for their temporariness. Thus we recognize the bounty which God has given us, while also recognizing our continued fragility and dependence on God.
During Hallel we shake the lulav during the following two verses:
הודו לה' כי טוב כי לעולם חסדו
אנא ה' הושיעה נא
One verse thanks God for the past; the other is a prayer for deliverance. A religious person will generally find it easy to do one or the other of these, depending on the circumstances. The hallmark of Sukkot is that we simultaneously do both.