That is, They who are the children of the flesh, these are not the children of God: but the children of the promise are counted for the descendants.
Read Chapter 9
Paul does not call them the children of Abraham, but rather “the children of God,” thus combining the past with the present and showing that even Isaac was not merely Abraham’s son. What Paul means is something like this: Whoever has been born in the way that Isaac was born is a son of God and of the seed of Abraham…. For Isaac was born not according to the law of nature nor according to the power of the flesh but according to the power of the promise.