The promises of God concern the spiritual descendants of Abraham:
Related Commentaries of Romans 9:6
Romans 9:6-9
6 Not as though the word of God hath taken none effect. For they are not all Israel, which are of Israel:
7 Neither, because they are the seed of Abraham, are they all children: but, In Isaac shall thy seed be called.
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.
9 For this is the word of promise, At this time will I come, and Sara shall have a son.