q.d. That I may speak more plainly, all those that are the children of Abraham according to the flesh, are not therefore the adopted children of God; it is not their blood, but their faith, must make them such. There are some of Abraham's seed, that are selected from the rest, to whom the promise was made, who are therefore called children of the promise; and of this sort are all they who are born after the Spirit, (as Isaac is said to be, Galatians 4:29), whether Jews or Gentiles. The sense of this verse is fully expressed, Galatians 3:8,14,29: see Galatians 4:28.
Related Commentaries of Romans 9:8
Romans 9:8
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.