John Chrysostom

Here again he lays low the lofty spirit of the Jews by reminding them of the time of the justification. And he well says, "the steps," that you as well as Abraham may believe in the resurrection of bodies that are dead. For he also displayed his faith upon this point. And so if you reject the uncircumcision, be informed for certain that the circumcision is of no more use unto you. For if you follow not in the steps of his faith, though you were ten thousand times in a state of circumcision, you will not be Abraham's offspring. …

Homily on Romans VIII ↗

Theophylact of Ohrid

Through circumcision Abraham proves to be the father of "the circumcision," that is, of the circumcised. Yet he is the father not only of those who have circumcision, but also of those who walk in the footsteps of the faith that he had while in uncircumcision. So, the present passage must be read thus: he became the father of the circumcised not for those who resemble him in circumcision alone, but for those who walk in the footsteps of his faith, that is, who like him believe in the resurrection of dead bodies. …

Commentary on Romans ↗

Irenaeus

Now, this Jesus did by drawing us off from the religion of stones, and bringing us over from hard and fruitless cogitations, and establishing in us a faith like to Abraham. As Paul does also testify, saying that we are children of Abraham because of the similarity of our faith, and the promise of inheritance.

Against Heresies Book IV ↗

Thomas Aquinas

Then he shows the manner in which he is the father even of the uncircumcised, namely, by imitation. And this is what he says: that he might be the father . . . not to those only who are of the circumcision, but to those also who follow the steps of the faith that is in the uncircumcision of our father Abraham, i.e., which Abraham had, while he was still uncircumcised: if you were Abraham's children, you would do what Abraham did (John 8:39).

Commentary on Romans ↗