John Calvin 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)

To them who are not, etc. The verb, are, is to be understood here as “are deemed to be,” for he refers to the carnal descendants of Abraham, who, having nothing but outward circumcision, confidently boasted in it. The other thing, which was the essential matter, they neglected, for they did not imitate the faith of Abraham, by which alone he obtained salvation. Therefore, it appears how carefully he distinguished between faith and the sacrament; not only so that no one might be satisfied with the one without the other, as though it were sufficient for justifying; but also so that faith alone might be presented as accomplishing everything: for while he allows the circumcised Jews to be justified, he expressly makes this exception—provided that in true faith they followed the example of Abraham; for why does he mention faith during uncircumcision, except to show that it alone is sufficient, without the aid of anything else? Let us then be careful that none of us, by improperly separating these matters, blend together the two modes of justification.

What has been stated also disproves the scholastic dogma concerning the difference between the sacraments of the Old and New Testaments, for they deny the power of justifying to the Old Testament sacraments and assign it to those of the New Testament. But if Paul reasons correctly when he argues that circumcision does not justify because Abraham was justified by faith, the same reasoning applies to us when we deny that people are justified by baptism, since they are justified by the same faith that Abraham had.