Thou believest that there is one God - One of the great and cardinal doctrines of religion is here selected as an illustration of all. The design of the apostle seems to have been to select one of the doctrines of religion, the belief of which would - if mere belief in any doctrine could - save the soul; and to show that even this might be held as an article of faith by those who could be supposed by no one to have any claim to the name of Christian. He selects, therefore, the great fundamental doctrine of all religion, - the doctrine of the existence of one Supreme Being, - and shows that if even this were held in such a way as it might be, and as it was held by devils, it could not save men. The apostle here is not to be supposed to be addressing such an one as Paul, who held to the doctrine that we are justified by faith; nor is he to be supposed to be combating the doctrine of Paul, as some have maintained, (see the Introduction); but he is to be regarded as addressing one who held, in the broadest and most unqualified sense, that provided there was faith, a man would be saved. To this he replies, that even the devils might have faith of a certain sort, and faith that would produce sensible effects on them of a certain kind, and still it could not be supposed that they had true religion, or that they would be saved. Why might not the same thing occur in regard to man?
Thou doest well - So far as this is concerned, or so far as it goes. It is a doctrine which ought to be held, for it is one of the great fundamental truths of religion.
The devils - The “demons,” - (τα δαιμόνια ta daimonia). There is, properly, but one being spoken of in the New Testament as “the devil” - ὁ διάβολος ho diabolos, and ὁ Σατᾶν ho Satan - though “demons” are frequently spoken of in the plural number. They are represented as evil spirits, subject to Satan, or under his control, and engaged with him in carrying out his plans of wickedness. These spirits or demons were supposed to wander in desert and desolate places, Matthew 12:43, or to dwell in the atmosphere, (Notes, Ephesians 2:2); they were thought to have the power of working miracles, but not for good, (Revelation 16:14; compare John 10:21); to be hostile to mankind, John 8:44; to utter the pagan oracles, Acts 16:17; to lurk in the idols of the heathen, 1 Corinthians 10:20; and to take up their abodes in the bodies of men, afflicting them with various kinds of diseases, Matthew 7:22; Matthew 9:34; Matthew 10:8; Matthew 17:18; Mark 7:29-30; Luke 4:33; Luke 8:27, Luke 8:30, et soepe. It is of these evil spirits that the apostle speaks when he says that they believe.
Also believe - That is, particularly, they believe in the existence of the one God. How far their knowledge may extend respecting God, we cannot know; but they are never represented in the Scriptures as denying his existence, or as doubting the great truths of religion. They are never described as atheists. That is a sin of this world only. They are not represented as sceptics. That, too, is a peculiar sin of the earth; and probably, in all the universe besides, there are no beings but those who dwell on this globe, who doubt or deny the existence of God, or the other great truths of religion.
And tremble - The word here used (φρίσσουσιν phrissousin) occurs nowhere else in the New Testament. It means, properly, to be rough, uneven, jaggy, sc., with bristling hair; to bristle, to stand on end, as the hair does in a fright; and then to shudder or quake with fear, etc. Here the meaning is, that there was much more in the case referred to than mere speculative faith. There was a faith that produced some effect, and an effect of a very decided character. It did not, indeed, produce good works, or a holy life, but it made it manifest that there was faith; and, consequently, it followed that the existence of mere faith was not all that was necessary to save men, or to make it certain that they would be secure, unless it were held that the devils would be justified and saved by it. If they might hold such faith, and still remain in perdition, men might hold it, and go to perdition. A man should not infer, therefore, because he has faith, even that faith in God which will fill him with alarm, that therefore he is safe. He must have a faith which will produce another effect altogether - that which will lead to a holy life.