ISB ~ Romans 3 v20

works of the law:Paul uses this expression eight times in his writings, twice in Romans (3:20, 28) and six times in Galatians (Gal 2:16; 3:2, 5, 10). Christian scholarship, both ancient and modern, has understood it in different ways. (1) Some, like St. Augustine, take it to mean observance of the entire Law of Moses, whole and undivided. On this view, Paul contends that no act of obedience to the moral, ceremonial, or juridical commandments of the Torah can bring about the justification of the sinner. (2) Others, like St. Jerome, understand the expression to mean the ceremoniai iaws of Moses, such as circumcision, dietary laws, feast days, and Sabbath observance. On this view, Paul charges that the ritual works of the Torah, which defined the Jewish way of life during the Mosaic age, have become obsolete in the New Covenant and thus have no bearing on justification.

Both views are correct in their proper context:initial justification in Baptism takes place apart from any observance of the Law whatever (Tit 3:4-7), whereas final justification at the Last Judgment takes place apart from the ceremonial works of the Law, but not apart from observing the moral commandments of the Law (Rom 2:13; Mt 19:16-19; 1 Cor 7:19; Jas 2:8-13).

knowledge of sin:Because the Torah defines what is good and evil, it acts as a moral informant and makes the sins of Israel stand out in stark clarity (2:17-23; 7:7; Heb 10:1-3).

See essay:The Works of the Law at Gal 3.