Centuries later the Holy Spirit inspired the Apostle Paul to write of this in his epistle to the Galatians, to which I will later refer.Isaac had become a young man, and God, to test Abraham, said: “Take your son your only son Isaac, whom you love, and go to the land of Moriah, and offer him there as a burnt offering on one of the mountains of which I shall tell you” (Genesis 22.2).The chart implies that shared human genealogy is of ultimate importance, but it is not.The two sons, half-brothers, share blood but not the ultimate purpose for which the one is chosen, the purpose to which I turn.And I will make of you a great nation, and I will bless you and make your name great, so that you will be a blessing.
Even the explanation of how in the person of Jesus this achievement would be realized is explicit in Isaac’s life.
I will establish my covenant with him as an everlasting covenant for his offspring after him.
As for Ishmael, I have heard you; behold, I have blessed him and will make him fruitful and multiply him greatly….
Having believed God, Abraham had immediate concern for the standing of his heir, Ishmael: “Oh that Ishmael might live before you!
God said, ‘No, but Sarah your wife shall bear you a son, and you shall call his name Isaac.