{9} Therefore to him that knoweth to do good, and doeth it not, to him it is sin.

(9) The conclusion of all the former treatise. The knowledge of the will of God does not only not at all profit, unless the life be answerable unto it, but also makes the sins far more grievous.

People's New Testament

4:17 To him that knoweth to do good, and doeth it not, to him it is sin. The connection of thought is probably as follows: I have warned you that such boasting is wrong, and that the right way is to speak submissively. If you know how to do the right and yet do it not, the sin is the greater on account of your knowledge. See Jas 4:15.

Wesley's Notes

4:17 Therefore to him that knoweth to do good and doeth it not - That knows what is right, and does not practise it. To him it is sin - This knowledge does not prevent, but increase, his condemnation.

Scofield Reference Notes

Margin sin

Sin. See Scofield Note: "Rom 3:23".

Jamieson-Fausset-Brown Bible Commentary

17. 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.

Matthew Henry's Concise Commentary

4:11-17 Our lips must be governed by the law of kindness, as well as truth and justice. Christians are brethren. And to break God's commands, is to speak evil of them, and to judge them, as if they laid too great a restraint upon us. We have the law of God, which is a rule to all; let us not presume to set up our own notions and opinions as a rule to those about us, and let us be careful that we be not condemned of the Lord. Go to now, is a call to any one to consider his conduct as being wrong. How apt worldly and contriving men are to leave God out of their plans! How vain it is to look for any thing good without God's blessing and guidance! The frailty, shortness, and uncertainty of life, ought to check the vanity and presumptuous confidence of all projects for futurity. We can fix the hour and minute of the sun's rising and setting to-morrow, but we cannot fix the certain time of a vapour being scattered. So short, unreal, and fading is human life, and all the prosperity or enjoyment that attends it; though bliss or woe for ever must be according to our conduct during this fleeting moment. We are always to depend on the will of God. Our times are not in our own hands, but at the disposal of God. Our heads may be filled with cares and contrivances for ourselves, or our families, or our friends; but Providence often throws our plans into confusion. All we design, and all we do, should be with submissive dependence on God. It is foolish, and it is hurtful, to boast of worldly things and aspiring projects; it will bring great disappointment, and will prove destruction in the end. Omissions are sins which will be brought into judgment, as well as commissions. He that does not the good he knows should be done, as well as he who does the evil he knows should not be done, will be condemned. Oh that we were as careful not to omit prayer, and not to neglect to meditate and examine our consciences, as we are not to commit gross outward vices against light!