Verse 7. Are they all children. Adopted into the true family of God. Many of the descendants of Abraham were rejected.

But in Isaac. This was the promise, Ge 21:12.

Shall thy seed, etc. Thy true people. This implied a selection, or choice; and, therefore, the doctrine of election was illustrated in the very commencement of the history of the nation; and as God had then made such a distinction, he might still do it. As he had then rejected a part of the natural descendants of Abraham, so he might, still do it. This is the argument which the apostle is pursuing.

{i} "In Isaac" Isa 55:11