Romans 4:12

And might be the father of circumcision. The apostle here tells them that Abraham is the father of all true believers, uncircumcised as well as circumcised, and all that believe in Christ, his seed, in whom God promised to bless all nations, are the spiritual sons of Abraham, and partake of the blessings promised to him in his posterity: nor can the circumcised be his true and spiritual children, unless they follow the footsteps of his faith, by which he was justified, when he believed the promises which God made to him before that circumcision was instituted; to wit, that he and Sara should have a son, when they were naturally past the age of having children, and that in his posterity all the world should be blessed, that is, in Christ. (Witham)