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.
8. That is, They are not, etc. He now gathers from God’s answer a proposition, which includes the whole of what he had in view. For if Isaac, and not Ishmael, was the seed, though the one as well as the other was Abraham’s son, it must be that all natural sons are not to be regarded as the seed, but that the promise is...
The apostle, having made his way to that which he had to say, concerning the rejection of the body of his countrymen, with a protestation of his own affection for them and a concession of their undoubted privileges, comes in these verses, and the following part of the chapter, to prove that the rejection of the Jews, by the establishment of the gospel dispensation, did...
Commenting on Romans 9:6-13
For this is the word of promise,.... The following passage is the Scripture, which contains the promise concerning the birth of Isaac; which was the produce, not of nature, but of divine grace and power; and was typical of the regeneration of God's elect, who "as Isaac was, are the children of promise", Gal 4:28, for as Ishmael was a type of them that are...