Romans 9:7-9 - Not all are children of Abraham

9:7

Paul goes back to Genesis and Abraham. First he points out that not all Abraham’s children were children of the promise. Isaac was a child of the promise, Ishmael was not. Paul expands greatly on this point in Gal 4:21-31. God made it quite clear to Abraham that it was through Isaac that His promises would be fulfilled, and no Jew would dispute this.

9:8,9

The point Paul is making is that natural descent has very little to do with it, and this has always been the case, it is not a newfangled idea. It is not the “children of the flesh” (i.e. by natural descent) that are children of God. It is children of the promise who are children of God. And God gave a specific promise about when Isaac would be born (Gen 17:21). Likewise, there was a specific time when the Messiah would come to earth.