Now ye rejoice Καυχασθε, ye glory, in your boastings Ye please yourselves in the vain thoughts which you entertain of these worldly projects and successes, and you boast of them. All such rejoicing Or glorying, is evil The delight you take in these expectations argues either a strange want of consideration, or gross stupidity. Therefore to him that knoweth to do good, and doeth it not That knows what is right and is his duty, and does not practise it; to him it is sin His knowledge does not prevent but increase his condemnation. As if he had said, Since you cannot but know better, as you have the oracles of God, and profess to believe them, if you do not act answerably thereto, you are guilty of the greater sin. “Because this is true with respect to all who act contrary to knowledge and conscience. Beza and Estius consider it as a general conclusion, enforcing the whole of the reproofs given to the Jews for acting contrary to the divine revelation, of which they were the keepers.” Macknight.
Related Commentaries of James 4:16
James 4:16-17
16 But now ye rejoice in your boastings: all such rejoicing is evil.
17 Therefore to him that knoweth to do good, and doeth it not, to him it is sin.