6 It is not as though the word of God had failed. For not all Israelites truly belong to Israel, 7 and not all of Abraham's children are his true descendants; but "It is through Isaac that descendants shall be named for you." 8 This means that it is not the children of the flesh who are the children of God, but the children of the promise are counted as descendants.
Matthew Henry's Commentary on Romans 9:6-8
Commentary on Romans 9:6-13
(Read Romans 9:6-13)
The rejection of the Jews by the gospel dispensation, did not break God's promise to the patriarchs. The promises and threatenings shall be fulfilled. Grace does not run in the blood; nor are saving benefits always found with outward church privileges. Not only some of Abraham's seed were chosen, and others not, but God therein wrought according to the counsel of his own will. God foresaw both Esau and Jacob as born in sin, by nature children of wrath even as others. If left to themselves they would have continued in sin through life; but for wise and holy reasons, not made known to us, he purposed to change Jacob's heart, and to leave Esau to his perverseness. This instance of Esau and Jacob throws light upon the Divine conduct to the fallen race of man. The whole Scripture shows the difference between the professed Christian and the real believer. Outward privileges are bestowed on many who are not the children of God. There is, however, full encouragement to diligent use of the means of grace which God has appointed.