John Chrysostom

He had shown that faith is necessary, that it is older than circumcision, that it is more mighty than the Law, that it establisheth the Law. For if all sinned, it was necessary: if one being uncircumcised was justified, it is older: if the knowledge of sin is by the Law and yet it was without the Law made evident, it is more mighty: if it has testimony borne to it by the Law, and establisheth the Law, it is not opposed to it, but friendly and allied to it. …

Homily on Romans VIII ↗

Theophylact of Ohrid

If the inheritance, he says, is given by the law, then "faith is made void," that is, it turns out to be vain and useless. For who would concern himself with faith if the promise of the inheritance were given by the law? But the state of affairs is not so. Abraham inherited the promise not by the law (for where was the law then?), but by faith, as it is written: "Abraham believed" (Gen. 15:6).

Commentary on Romans ↗

Thomas Aquinas

Then when he says, for if they, he proves his statement: first, in regard to the denial that the promise is to be fulfilled through the law; second, in regard to the assertion that it is to be fulfilled through the justice of faith, at therefore it is of faith (Rom 4:16). In regard to the first he presents this argument: if the promise made to Abraham were to be fulfilled through the law, Abraham's faith believing the promise would be null, because the promise made to him would be abolished. But this is not fitting. …

Commentary on Romans ↗