Theophylact of Ohrid, on Jas 4:17

“To him therefore who knoweth to do good, and doth it not, to him it is sin.”

“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.”

Imported from an open dataset — not yet checked against the printed edition.