Romans 9:8

Romans 9:8. That is; the Old Testament saying amounts to this.

Not they who are the children of the flesh, are children of God. Not those who must be regarded merely as the fruit of physical generation, as was the case with Ishmael (comp. Galatians 4:23).

But the children of the promise are reckoned as seed. The reference is directly to the birth of Isaac (Romans 9:9), but also to his true descendants, who ‘are reckoned' such in virtue of the promise. The birth of Isaac was not only according to the promise, but God intervened through the promise, which Abraham believed, and thus by his faith in the promise obtained the power that rendered him capable of becoming the father of this son (comp. chap. Romans 4:16-21). ‘In virtue of this superior element, Isaac and his descendants alone could be regarded as “children of God.” It is this which explains the second proposition of the verse, where the title of (promised) posterity is expressly given to that descent obtained through faith in the promise. The first proposition of the verse by implication justifies the rejection of carnal Jews; the second, the adoption of believing Gentiles' (Godet).