5To them belong the patriarchs, … It was from Israel that the primary recipients of God’s promises flow. This would include Abraham, Isaac, Jacob and his twelve sons. And from their race, according to the flesh, is the Christ… Paul reaffirms that Christ too had come forth as a descendent of Abraham and David, alluding to Romans 15: 8 where he explicitly teaches that Christ came to show God’s faithfulness in fulfilling His promises to the patriarchs. Who is God over all, blessed forever. Amen….Paul reminds his readers of the divinity of Christ, mentioning that Christ glories and is God over all, not just of ethnic Israel.
6But it is not as though the word of God has failed…Here Paul turns to the basic issue that had already been mention in the beginning of this paper. No doubt that God’s faithfulness in keeping His promises to the Patriarchs is being called into question and Paul seeks to defend the righteousness and the Sovereignty of God in keeping with His word in the following section. For not all who are descended from Israel belong to Israel,…Paul explains that God had never promised the certainty of the salvation of all ethnic Israel, but there are some descendents from ethnic Israel that are not a part of the true Israel. It follows from this then that the existence of a multitude of unbelievers in ethnic Israel does not mean the promises of God had been thwarted, neither has the word of God failed.
7and not all are children of Abraham because they are his offspring…By mentioning Abraham, Paul argues that the true Israel are those who receive justification by faith alone, which he had already argued in Romans chapter four. but “Through Isaac shall your offspring be named.”… This is a quotation from Genesis 21:12. The context of this quotation is God telling Abraham to allow Sarah to throw out Hagar and Ishmael, confirming that not all of the flesh offspring of Abraham are of the true Israel.
8This 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… Paul argues that it is the spiritual offspring of Abraham that is the true Israel; those who believe, by faith, in the promises of God. Hence, if Isaac was the seed, Ishmael was not, and Jacob was the seed while Esau was passed over, it follows that not all of Abraham’s natural descendents are of the True Israel. Paul is also making a comparison to chapter 4:11-18, where Paul states that Abraham is the father of all who believes by faith. This inheritance is not given through the flesh or from the law, but a spiritual inheritance received by having faith on the promises of God.