The former verse tells you he was the father of the believing Gentiles, for the covenant was made with him, for all his believing seed, when he was uncircumcised, which shows, that righteousness is and may be imputed to them also without any outward circumcision: and then he is the father of the believing Jews; especially of as many of them as unto circumcision do add the imitation of his faith; who, besides circumcision, which they derived from him, do also transcribe his divine copy, and follow his example of faith and obedience; who leave their sins, as he did his country; who believe all God's promises, and adhere to him against all temptations to the contrary.
Related Commentaries of Romans 4:12
Romans 4:12
12 And the father of circumcision to them who are not of the circumcision only, but who also walk in the steps of that faith of our father Abraham, which he had being yet uncircumcised.