{10} Thou believest that there is one God; thou doest well: the devils also believe, and tremble.

(10) Another reason taken from an absurdity: if such a faith were the true faith by means of which we are justified, the demons would be justified, for they have that, but nonetheless they tremble and are not justified, therefore neither is that faith a true faith.

People's New Testament

2:19 Thou believest that there is one God. That is very well, but can that alone save you?

The devils also believe, and tremble. Even the demons believe that also. See Mt 8:29. Evil spirits confessed Christ, but this confession of faith did not save them.

Wesley's Notes

2:19 Thou believest there is one God - I allow this: but this proves only that thou hast the same faith with the devils. Nay, they not only believe, but tremble - At the dreadful expectation of eternal torments. So far is that faith from either justifying or saving them that have it.

Jamieson-Fausset-Brown Bible Commentary

19. Thou-emphatic. Thou self-deceiving claimant to faith without works.

that there is one God-rather, "that God is one": God's existence, however, is also asserted. The fundamental article of the creed of Jews and Christians alike, and the point of faith on which especially the former boasted themselves, as distinguishing them from the Gentiles, and hence adduced by James here.

thou doest well-so far good. But unless thy faith goes farther than an assent to this truth, "the evil spirits (literally, 'demons': 'devil' is the term restricted to Satan, their head) believe" so far in common with thee, "and (so far from being saved by such a faith) shudder (so the Greek)," Mt 8:29; Lu 4:34; 2Pe 2:4; Jude 6; Re 20:10. Their faith only adds to their torment at the thought of having to meet Him who is to consign them to their just doom: so thine (Heb 10:26, 27, it is not the faith of love, but of fear, that hath torment, 1Jo 4:18).

Matthew Henry's Concise Commentary

2:14-26 Those are wrong who put a mere notional belief of the gospel for the whole of evangelical religion, as many now do. No doubt, true faith alone, whereby men have part in Christ's righteousness, atonement, and grace, saves their souls; but it produces holy fruits, and is shown to be real by its effect on their works; while mere assent to any form of doctrine, or mere historical belief of any facts, wholly differs from this saving faith. A bare profession may gain the good opinion of pious people; and it may procure, in some cases, worldly good things; but what profit will it be, for any to gain the whole world, and to lose their souls? Can this faith save him? All things should be accounted profitable or unprofitable to us, as they tend to forward or hinder the salvation of our souls. This place of Scripture plainly shows that an opinion, or assent to the gospel, without works, is not faith. There is no way to show we really believe in Christ, but by being diligent in good works, from gospel motives, and for gospel purposes. Men may boast to others, and be conceited of that which they really have not. There is not only to be assent in faith, but consent; not only an assent to the truth of the word, but a consent to take Christ. True believing is not an act of the understanding only, but a work of the whole heart. That a justifying faith cannot be without works, is shown from two examples, Abraham and Rahab. Abraham believed God, and it was reckoned unto him for righteousness. Faith, producing such works, advanced him to peculiar favours. We see then, ver. 24, how that by works a man is justified, not by a bare opinion or profession, or believing without obeying; but by having such faith as produces good works. And to have to deny his own reason, affections, and interests, is an action fit to try a believer. Observe here, the wonderful power of faith in changing sinners. Rahab's conduct proved her faith to be living, or having power; it showed that she believed with her heart, not merely by an assent of the understanding. Let us then take heed, for the best works, without faith, are dead; they want root and principle. By faith any thing we do is really good; as done in obedience to God, and aiming at his acceptance: the root is as though it were dead, when there is no fruit. Faith is the root, good works are the fruits; and we must see to it that we have both. This is the grace of God wherein we stand, and we should stand to it. There is no middle state. Every one must either live God's friend, or God's enemy. Living to God, as it is the consequence of faith, which justifies and will save, obliges us to do nothing against him, but every thing for him and to him.