7 Nor because they are his descendants are they all Abraham's children. On the contrary, "It is through Isaac that your offspring will be reckoned."[1] 8 In other words, it is not the children by physical descent who are God's children, but it is the children of the promise who are regarded as Abraham's offspring.
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.
7 and not all are children of Abraham because they are his offspring, but "Through Isaac shall your offspring be named." 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 offspring.
7 It wasn't Abraham's sperm that gave identity here, but God's promise. Remember how it was put: "Your family will be defined by Isaac"? 8 That means that Israelite identity was never racially determined by sexual transmission, but it was God-determined by promise.
7 nor are they all children because they are the seed of Abraham; but, "In Isaac your seed shall be called." 8 That is, those who are the children of the flesh, these are not the children of God; but the children of the promise are counted as the seed.
7 Being descendants of Abraham doesn't make them truly Abraham's children. For the Scriptures say, "Isaac is the son through whom your descendants will be counted," though Abraham had other children, too. 8 This means that Abraham's physical descendants are not necessarily children of God. Only the children of the promise are considered to be Abraham's children.
Matthew Henry's Commentary on Romans 9:7-8
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.