The covenant is with Isaac

The text

¹⁹God said, “No, but Sarah, your wife, will bear you a son. You shall call his name Isaac. I will establish my covenant with him for an everlasting covenant for his offspring after him. ²⁰As for Ishmael, I have heard you. Behold, I have blessed him, and will make him fruitful, and will multiply him exceedingly. He will become the father of twelve princes, and I will make him a great nation. ²¹But I will establish my covenant with Isaac, whom Sarah will bear to you at this set time next year.”

Genesis 17:19-21 (WEB) · context

¹²God said to Abraham, “Don’t let it be grievous in your sight because of the boy, and because of your servant. In all that Sarah says to you, listen to her voice. For your offspring will be named through Isaac. ¹³I will also make a nation of the son of the servant, because he is your child.”

Genesis 21:12-13 (WEB) · context

²Yahweh appeared to him, and said, “Don’t go down into Egypt. Live in the land I will tell you about. ³Live in this land, and I will be with you, and will bless you. For I will give to you, and to your offspring, all these lands, and I will establish the oath which I swore to Abraham your father. ⁴I will multiply your offspring as the stars of the sky, and will give all these lands to your offspring. In your offspring all the nations of the earth will be blessed, ⁵because Abraham obeyed my voice, and kept my requirements, my commandments, my statutes, and my laws.”

Genesis 26:2-5 (WEB) · context

¹³Behold, Yahweh stood above it, and said, “I am Yahweh, the God of Abraham your father, and the God of Isaac. I will give the land you lie on to you and to your offspring. ¹⁴Your offspring will be as the dust of the earth, and you will spread abroad to the west, and to the east, and to the north, and to the south. In you and in your offspring, all the families of the earth will be blessed.

Genesis 28:13-14 (WEB) · context

The New Testament reading

⁷Neither, because they are Abraham’s offspring, are they all children. But, “your offspring will be accounted as from Isaac.” ⁸That is, it is not the children of the flesh who are children of God, but the children of the promise are counted as heirs.

Romans 9:7-8 (WEB) · context

²²For it is written that Abraham had two sons, one by the servant, and one by the free woman. ²³However, the son by the servant was born according to the flesh, but the son by the free woman was born through promise. ²⁴These things contain an allegory, for these are two covenants. One is from Mount Sinai, bearing children to bondage, which is Hagar. ²⁵For this Hagar is Mount Sinai in Arabia, and answers to the Jerusalem that exists now, for she is in bondage with her children. ²⁶But the Jerusalem that is above is free, which is the mother of us all. ²⁷For it is written, “Rejoice, you barren who don’t bear. Break out and shout, you who don’t travail. For the desolate women have more children than her who has a husband.” ²⁸Now we, brothers, as Isaac was, are children of promise.

Galatians 4:22-28 (WEB) · context

⁷Know therefore that those who are of faith are children of Abraham. ⁸The Scripture, foreseeing that God would justify the Gentiles by faith, preached the Good News beforehand to Abraham, saying, “In you all the nations will be blessed.” ⁹So then, those who are of faith are blessed with the faithful Abraham.

Galatians 3:7-9 (WEB) · context