Charles Ellicott Commentary Romans 4:12

"and the father of circumcision to them who not only are of the circumcision, but who also walk in the steps of that faith of our father Abraham which he had in uncircumcision." — Romans 4:12 (ASV)

On the other hand, the mere performance of the rite was no guarantee of justification, unless it was accompanied by a faith like Abraham’s. Of these two—faith itself, and circumcision (the sign of faith)—only the first was essential, and the second was useless without it.

On verses 9-12:

What is the significance of this for the relationship between Jew and Gentile? Is the blessedness of the justified state reserved only for the former? Is it limited to those who are circumcised? On the contrary, the state of justification was attributed to Abraham himself before he was circumcised. Justification is the result of faith, not of circumcision. Circumcision is so far from superseding faith that it was only its sign or seal.

This, then, is the great test. Those who have this faith may hope for justification, whether their descent from Abraham is spiritual or literal.