The story of the sale of the birthright is one of the strangest stories in all of the Torah. Why does Yaakov want to buy the birthright? Can a birthright really be 'bought' or 'sold'? Is Yaakov exploiting Esav's weak state, forcing him to sell the birthright against his will?
By closely examining this story and the stories in all of Sefer Bereishit, we notice that one of the most important themes of Sefer Bereishit is the matter of Divine chosenness. Throughout the Sefer we grapple with the question of who is chosen. Who is God choosing to represent God's way in the world? And throughout the Sefer, the one who is chosen is not the firstborn. The entire Sefer teaches that the physical fact of being the eldest does not automatically ensure the right to the firstborn blessing. God chooses the person who is worthy of receiving the blessing. God's blessing is given on the basis of merit, not chronology.