John Chrysostom

"For by the Law is the knowledge of sin." He springs upon the Law again, with forbearance however (for what he says is not an accusation of it, but of the listlessness of the Jews). Yet nevertheless he has been earnest here with a view (as he was going to introduce his discourse about faith) to show its utter feebleness. For if thou boastest in the Law, he means, it puts thee to the greater shame: it solemnly parades forth your sins before you. …

Homily on Romans 7 ↗

Theophylact of Ohrid

The Apostle does not mean that they sinned so that their mouths would be stopped; but they were reproved by the prophets so that they would not present their sins as sins of ignorance and boast. And not only the Jews, but "the whole world becomes guilty before God," that is, condemned, lacking boldness, not justified by their own works, but in need of outside help, that is, the grace of Christ. …

Commentary on Romans ↗

Clement of Alexandria

How, then, is the law still said to be not good by certain heresies that clamorously appeal to the apostle, who says, "For by the law is the knowledge of sin?" To whom we say, The law did not cause, but showed sin. For, enjoining what is to be done, it reprehended what ought not to be done. And it is the part of the good to teach what is salutary, and to point out what is deleterious; and to counsel the practice of the one, and to command to shun the other. …

The Stromata Book 2 ↗

Thomas Aquinas

Then when he says because by the works of the law, he assigns the reason for these words: first, he assigns the reason; second, he explains it, at for by the law. First, therefore, he says: the reason there is not any man just is that no flesh shall be justified before him, i.e., according to his judgment, by the works of the law; because, as is stated in Galatians: if justification were through the law, then Christ died to no purpose (Gal 2:21), and in Titus: not because of deeds done by us in justice, but in virtue of his own mercy …

Commentary on Romans ↗

Bernard of Clairvaux

There is a charity in act, and there is one in affection. And concerning that which is of work, I think the law was given to men and a commandment was formed: for who so possesses it in affection as it is commanded? Therefore the one is commanded for merit, the other is given as a reward. We do not deny that divine grace can grant its beginning indeed, and its progress, to be experienced even in the present life; but its consummation we firmly reserve for future happiness. …

Sermons on the Song of Songs, Sermon 50 ↗