But it is not as though the word of God has come to nothing. For they are not all Israel that are of Israel. Neither, because they are Abraham’s offspring, are they all children. But, “your offspring will be accounted as from Isaac.” That is, it is not the children of the flesh who are children of God, but the children of the promise are counted as heirs. For this is a word of promise: “At the appointed time I will come, and Sarah will have a son.”