Towards the beginning of Parashat Toledot, we read of the "sale" of Esav's "bekhora" (birthright) to Yaakov. This incident raises many questions, which have been dealt with by both Biblical commentators as well as halakhists. For one thing, scholars have discussed the legal significance of this sale. The privileges associated with the birthright take effect only upon the father's death; as such, these privileges fall under the halakhic category of "davar she-lo ba la-olam" – something that has yet to come into one's possession. According to Halakha, one does not have the legal power to sell such an item, and such a sale is thus legally meaningless. Additionally, writers have had to grapple with the moral problem that arises from this sale. The Torah describes Esav as returning home weary and famished from the hunt, to the point where Esav exclaims, "Behold, I am going to die!" (25:32; see Rashi, however, for a much different explanation of this sentence). Does not Yaakov take unfair advantage of his brother's hunger, by demanding the eternal birthright in exchange for a bowl of lentils?
These and other questions concerning this episode are immediately resolved if we accept the approach taken by Rav Shimshon Refael Hirsch and Rav David Tzvi Hoffman to this entire narrative. Based on a passage in the Midrash referring to the brothers' conduct in this story as "mesachakim" – "playing," these commentators argue that this "sale" was never intended as a serious, legally binding exchange. Never do we find Yaakov pointing to this incident as a basis for his right to his father's blessing or to any other privilege. Quite to the contrary, later in the parasha, we find Yaakov initially refusing to go along with his mother's plot to seize his father's blessing from Esav, and he finally agrees only reluctantly, out of respect for his mother's wishes. The "sale" of the birthright is actually no more than childish games between two brothers.
Why, then, does the Torah bother recording this incident? This story reveals and exemplifies the different orientations that Esav and Yaakov began to develop as they reached adolescence. As Rav Hirsch writes, Yaakov's "demand" that Esav sell him the birthright in fact expressed his desire to inherit the legacy of Avraham and Yitzchak, a desire that paralleled Esav's craving for food at that moment. Rav Hirsch adds that this contrast between Yaakov because even more acute in light of Chazal's comment that Avraham had died that day (see Rashi, 25:30). As Esav spends the day hunting, Yaakov begins to ponder the future of Avraham's legacy and wonder what will happen when it is Yitzchak, rather than Avraham, who passes away. And thus when Esav returns home and asks for nothing but food, Yaakov has on his mind the future of Avraham's spiritual teachings.
The purpose of this narrative, then, is not the legal repercussions of this sale, but rather the fundamental difference in the brothers' orientation that it reveals.