“Swear to me first,” Jacob said. So Esau swore to Jacob and sold him the birthright.
33. And Jacob said, Swear to me. Jacob did not act cruelly towards his brother, for he took nothing from him, but only desired a confirmation of that right which had been divinely granted to him; and he does this with a pious intention, that he may hereby the more fully establish the certainty of his own election.
We have here a bargain made between Jacob and Esau about the birthright, which was Esau's by providence but Jacob's by promise. It was a spiritual privilege, including the excellency of dignity and the excellency of power, as well as the double portion, Gen 49:3. It seemed to be such a birthright as had then the blessing annexed to it, and the entail of the promise. Now see, I.
Commenting on Genesis 25:29-34
And Jacob said, swear unto me this day,.... For the more sure and certain confirmation of the bargain; and by this oath oblige himself to let him peaceably enjoy the birthright, nor seek to revoke it, or dispute it with him, or disturb him in the possession of it: and he sware unto him; that he would abide by the bargain, and never give him...