Jas 4:17

“To him therefore who knows to do good and does not do it, it is sin. Throughout the text of this Epistle, the blessed James shows that those to whom he wrote had the knowledge of doing good, and had also learned the right faith, so that they had presumed they could become teachers to others, yet had not attained the perfection of works, or humility of mind, or even moderation of speech. Hence, he now among other words of reproof and exhortation greatly frightens them with this statement, that he who knows how to do good, and does not do what he knows, is said to have a greater sin than he who sins out of ignorance. Although he who sins in ignorance cannot be entirely free from guilt, for ignorance of good itself is not a small evil. Hence the Lord said: The servant who knew his master's will, and did not prepare himself or do according to his will, shall be beaten with many stripes. But he who did not know, yet committed things deserving of stripes, shall be beaten with few (Luke 12).”

“He again takes up the subject of vain arrogance, which usually arises from pride, and as if concluding the discourse, says that boasting is evil. If it is evil, then it proceeds without doubt from the evil one. But those who through holy baptism have given themselves over to the Lord should not accept what is sown by the evil one. He adds also this: "to him who knows to do good and does not do it, to him it is sin" (Jas. 4:17). Again he admonishes the false teachers not to dare to teach what they themselves have not first practiced, for blessed, it is said, is not the one who teaches, but the one "who does and teaches" (Matt. 5:19), since deeds must precede words, by which the righteous man also proclaims the faith he manifests. For whoever, says the Lord, breaks one of these least commandments and teaches men so — that is, teaches that which he himself has not labored at — shall be called least... "but whoever does and teaches them, he shall be called great" (Matt. 5:19). Therefore the God-man Himself first began to do and then to teach (Acts 1:1). Such, in my opinion, is the thought also in these words: "He who glories, let him glory in the Lord" (1 Cor. 1:31) — that is, as one like the Lord, having in Him a teacher and example. Similarly, David says: "In the Lord shall my soul boast" ("My soul shall make its boast in the Lord") (Ps. 34:2) — saying nothing other than this: I would wish to boast in that I walk according to the commandments of the Lord.”

“The general principle illustrated by the particular example just discussed is here stated: knowledge without practice is imputed to a man as great and presumptuous sin. James reverts to the principle with which he started. Nothing more injures the soul than wasted impressions. Feelings exhaust themselves and evaporate, if not embodied in practice. As we will not act except we feel, so if we will not act out our feelings, we shall soon cease to feel. Next: James Chapter 5”