Romans 3:20 - Clarke's commentary and critical notes on the Bible

Therefore by the deeds of the law there shall no flesh be justified in his sight: for by the law is the knowledge of sin. Therefore, by the deeds of the law - On the score of obedience to this moral law, there shall no flesh, ου πασα σαρξ, no human being, be justified; none can be accepted in the sight of God. And why? Because by the law is the knowledge of sin: it is that which ascertains what sin is; shows how men have deviated from its righteous demands; and sentences them to death because they have broken it. Thus the law is properly considered as the rule of right; and, unless God had given some such means of discovering what Sin is, the darkened heart of man could never have formed an adequate conception of it. For, as an acknowledged straight edge is the only way in which the straightness or crookedness of a line can be determined, so the moral obliquity of human actions can only be determined by the law of God; that rule of right which proceeds from his own immaculate holiness.