"After the death of Abraham, God blessed his son Isaac; and Isaac dwelt by the well Lahai-roi." (Genesis 25:11) When Isaac was about sixty years old there were born to him and his wife Rebekah two sons, twins, who were named by them Esau and Jacob .-- Genesis 25:26.
[106]Isaac then went to live in the land of the Philistines, and while there, God said to him: "Sojourn in this land, and I will be with thee, and will bless thee; for unto thee, and unto thy seed, I will give all these countries, and I will perform the oath which I sware unto Abraham thy father; and I will make thy seed to multiply as the stars of heaven, and will give unto thy seed these countries; and in thy seed shall all the nations of the earth be blessed".

(Genesis 26:3,4) Thus the Abrahamic promise was renewed to Isaac.

Before the death of Isaac, he pronounced his blessing upon his son Jacob, and Jacob thereby became the successor of his father to the Abrahamic promise.
[107]Under the rule of descent, the firstborn or eldest son was the heir of the father's estate and any other rights or privileges that went with that estate, unless for some cause there should be an exception to the rule.

Esau having been born a few moments before his brother Jacob, under the operation of this rule would be the successor to the Abrahamic promise and heir to his father.

His birthright, therefore, would include the promise made to Abraham.