When Rivka was suffering through her painful pregnancy, ותלך לדרש את השם, "she went to inquire of Hashem." The response informed her that שני גיים בבטנך, "there are two nations in your womb." The Torah uses an unusual spelling for the word "nations" in this verse, a spelling which indicates "pride." Rashi offers an Midrashic explanation:
This refers to Antoninus and Rebbe [Yehuda HaNasi], whose tables never lacked for radish or lettuce, neither in the summer nor during the rainy season. (Avoda Zara 11)Rivka is told a prophecy. Within her womb she carries the fathers of two proud nations, nations that will be blessed with leaders of great power and wealth.
As the boys grow up, Rivka sees that the two boys have very different natures. "Eisav was a man who knew how to hunt, a man of the field, and Yaakov was a man of sincerity who sat [studying] in tents" (25:27). Rivka understands that prophecy is not merely for inquiring minds. Prophecy is a mandate and the recipient must act to see it through. It is easy to see that Eisav was gifted with the genes of a leader, he has the skills and talents for power and wealth. Yaakov, on the other hand, lacks these talents and he will need his father's blessings to make his destiny a reality.
The prophecy Rivka received before her sons were born is what gave her the license to direct the blessings of wealth and power to Yaakov.
This explanation also resolves a different problem. As Rashi tells us repeatedly, he is focused exclusively on פשט, the straightforward meaning of the text. To paraphrase Rashi's own words, if you are interested in reading Midrash, you can find it on the shelf (cf. Rashi to Bereishis 3:8). Why then does Rashi quote this Midrash about Antoninus and Rebbe? The answer is that this interpretation of the prophecy is the only way to explain Rivka's subsequent behavior!
Yaakov does as he is told, but he's clearly not happy about it. Beyond the obvious ethical problems that this scheme raises for the man of truth, there is another issue here of no less import. For, as we have seen, Eisav's mission is bound up with his blessing. It follows that to steal the blessing of the man of the field is to take on the responsibilities of the man of the field - responsibilities that Yaakov, the יושב אהלים, would understandably prefer to avoid. We present here several pieces of evidence:
Yaakov's use of אולי for "maybe" is significant. According to the Vilna Gaon, אולי is used when the speaker hopes that the issue in doubt will come true [if you hope it won't, פן is used](Gaon on Bereishis 24:39, see Kol Eliyahu for examples). Based on this Gaon, Rabbi Yitzchok Dov Bamberger (Wurzburger Rov, 1807-1878) explains that despite his mother's orders, Yaakov secretly hoped the ruse would be foiled by his father (cited in Peninim MiShulchan HaGra).
ותקח רבקה את בגדי עשו בנה הגדל החמדת... ותלבש את יעקב בנה הקטן
Rivkah has to dress Yaakov herself to get him to participate! Indeed, the Midrash tells us that Yaakov cried as his fulfilled his mother's orders (B.R. 65:15).
We must note that Yaakov forces the angel of Eisav to recognize his right to the berachos (Rashi to 32:27) and demands that he do so immediately (Rashi to 32:29). In the end, Eisav himself explicitly cedes the berachos to his brother! (Rashi 33:9)