birthright
The "birthright" had three elements:
(1) Until the establishment of the Aaronic priesthood the head of the family exercised priestly rights.
(2) The Abrahamic family held the Edenic promise of the Satan-Bruiser (Genesis 3:15). -- Abel, Seth, Shem, Abraham, Isaac, Esau.
(3) Esau, as the firstborn, was in the direct line of the Abrahamic promise of the Earth-Blesser (Genesis 12:3).
For all that was revealed, in Esau might have fulfilled those two great Messianic promises. This birthright Esau sold for a momentary fleshly gratification. Jacob's conception of the birthright at that time was, doubtless, carnal and inadequate, but his desire for it evidenced true faith.