Genesis 17:19: "And God said, Sarah thy wife shall bear thee a son indeed; and thou shalt call his name Isaac: and I will establish my covenant with him for an everlasting covenant, and with his seed after him."
Romans 9:6: "Not as though the word of God hath taken none effect. For they are not all Israel, which are of Israel:"
Romans 9:7: "Neither, because they are the seed of Abraham, are they all children: but, In Isaac shall thy seed be called."
Romans 9:8: "That is, They which are the children of the flesh, these are not the children of God: but the children of the promise are counted for the seed."