Albert Barnes 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)

And the father of circumcision, the father, that is, the ancestor, exemplar, or model of those who are circumcised, and who possess the same faith that he did. Not only the father of all believers (Romans 4:11), but, in a special sense, the father of the Jewish people. In this, the apostle suggests that though all who believed would be saved as he was, yet the Jews had a special proprietorship in Abraham; they had special favors and privileges from the fact that he was their ancestor.

Not of the circumcision only. Who are not merely circumcised, but who possess his spirit and his faith. Mere circumcision would not be sufficient; but circumcision, connected with faith like his, showed that they were peculiarly his descendants (see the notes on Romans 2:25).

Who walk in the steps, etc. Who embrace his example; who embrace his spirit; who have his faith.

Being yet uncircumcised. Before he was circumcised. Compare Genesis 15:6 with Genesis 17.