|ועתה שא נא כליך תליך וקשתך, וצא השדה, וצודה לי ציד.||הביאה לי ציד|
|ועשה לי מטעמים כאשר אהבתי||ועשה לי מטעמים|
|והביאה לי ואכלה||ואכלה|
|בעבור תברכך נפשי||ואברככה|
|בטרם אמות.||לפני מותי.|
Rivkah's description is very accurate. Everything that Yitzchak said she repeats in more efficient language.
But there is also one thing she adds, which wasn't in Yitzchak's statement: the words "lifnei Hashem".
This change seems to reflect a deep misunderstanding between Yitzchak and Rivkah regarding the purpose of the blessing. Looking at the text of the blessing which Yitzchak thought he was giving to Esav, we see it is all about material success. The "consolation" blessing which Esav gets later is also about material success. In contrast, Yitzchak's blessing to Yaakov (28:3-4) speaks of Yaakov's receiving "the blessing of Avraham" - the spiritual inheritance which was passed down through the Avot and later through the Jewish people. Yitzchak never intended to bless Esav "before God". Both Esav and Yaakov were to be blessed, but only Yaakov's blessing was to be "before God".
Rivkah did not realize that this was Yitzchak's intention. She thought there would be only one blessing - which, by necessity, would be spiritual. And of course, only Yaakov could be the correct recipient for this blessing. Thus she inserted the words "lifnei Hashem" which Yitzchak had, in fact, purposefully refrained from using.
The misunderstanding between Yitzchak and Rivkah is part of a chain of events which resonates throughout Jewish history. Rivkah's misunderstanding led Yaakov to take Esav's blessing, which forced Yaakov to flee penniless to Haran, which allowed Lavan to trick Yaakov, which forced Yaakov to take two mutually antagonistic wives, which led to bitter conflict between Yaakov's children, which resulted in Yosef's sale to Egypt, which eventually caused the entire family to descend to Egypt and enter slavery.
I would like to extend this chain of causation in the other direction, back to God's promise to Avraham that "your offspring will be strangers in a land not theirs, and shall serve them..." (15:13) In the immediate aftermath of the Akedah (22:19) we hear that "Avraham" returns to Beer Sheva. Presumably Yitzchak is with him, but the lack of mention hints at a disconnect between them. Perhaps we may say that Yitzchak was permanently traumatized by the Akedah. Having his trust in his father so violently betrayed, he was unable to fully trust in anyone else for the rest of his life. The most notable consequence of this lack of trust was the misunderstanding over Yaakov and Esav's blessings.
If so, then we can trace the prophecy's inexorable progression through the generations, from Avraham's lifetime until its eventual fulfillment centuries later. While none of the characters involved could have realized what they were doing, in the end each of them contributed to the fulfillment of the Divine plan.
As Yosef says to his brothers, "You planned to do evil to me, yet God planned that it be for good, so that I might now save the lives of many people." (45:5) But even Yosef perceived only one small fraction of his contribution: the temporary escape from famine, but not the eventual enslavement and redemption which would follow from his descending to Egypt.
This is the book of generations of man: When God created man, He made him in the image of God. Male and female he made them, and he called them Adam/Mankind when He created them. Adam lived 130 years... [begin genealogy] (Breishit 5:1-3)
These are the generations of Yitzchak son of Avraham; Avraham begot Yitzchak. Yitzchak was 40 years old when he took Rivkah - daughter of Betuel the Aramean from Padan-Aram, sister of Lavan the Aramean - as his wife. Yitzchak entreated Hashem regarding his wife, since she was barren... (25:19-21)
What do these two selections have in common? 1) They are both "These-are-the-generations" formulas, indicating of the beginning of two of the sections of Sefer Breishit. 2) They both include a couple lines of background information, well-known from the previous stories, before the "real" story.
It seems that each "generations" section is intended to be self-contained. Therefore, each section begins with a brief summary of the necessary background information - the creation of man, and the marriage of Yitzchak and Rivkah, respectively. Perhaps you have read the preceding chapters and know this information already. But stylistically, in order to make clear that it is distinct from the other sections, each section assumes that perhaps you haven't.
These are the generations of Yitzchak son of Avraham; Avraham begot Yitzchak. (25:19)
Why must Avraham be mentioned (twice!) as Yitzchak's father? I think this is because - contrary to all expectations, due to Avraham's importance to the story - there is no section of Sefer Breishit entitled "These are the generations of Avraham". To account for this "gap" in the section headers, Avraham is mentioned in the headers of his sons - Yitzchak here, and Yishmael in 25:12. (Other than Yishmael and Yitzchak, no person's "generations" in Sefer Breishit mention their father.)
Yitzchak brought her to the tent of Sarah his mother. He took Rivkah and she became his wife, and Yitzchak was comforted after his mother['s death]. (24:67)
Rivkah took the best clothes of Esav her older son, which were with her in the house, and dressed Yaakov her younger son. (27:15)
When she first married Yitzchak, Rivkah was living in a tent, like Avraham and Sarah had. But by the time Yitzchak grew old enough to bless his kids, she was now living in a house.
If we look throughout Sefer Breishit, the term "house of" is used many times to refer to a person's family. But as far as I know, verse 27:15 is the only time when it is used regarding a physical structure. Sefer Breishit mentions over and over that Avraham and Yaakov were living in tents. Here we see that, by the end of his life, Yitzchak was living in a not a tent but a house.
As R' Amnon Bazak explains in an incredible article, Yitzchak succeeded in several ways in which Avraham (and Yaakov) did not. One of these areas was in asserting his connection and right to the land of Israel. We see this in the fact that Yitzchak does not offer to divide the land with someone else (i.e. Lot), nor does he make a covenant with the land's non-Jewish inhabitants (i.e. Avimelech). We see further evidence here, where instead of moving from tent to tent like a nomad, Yitzchak builds an immovable and permanent "house" which demonstrates the strength of his connection to the land.