Do not err. This is an argument from what is opposite; for as God is the author of all good, it is absurd to suppose him to be the author of evil. To do good is what properly belongs to him, and according to his nature; and from him all good things come to us. Then, whatever evil he does, is not agreeable to his nature. But as it sometimes happens, that he who quits himself well through life, yet in some things fails, he meets this doubt by denying that God is mutable like men. But if God is in all things and always like himself, it hence follows that well-doing is his perpetual work. This reasoning is far different from that of Plato, who maintained that no calamities are sent on men by God, because he is good; for though it is just that the crimes of men should be punished by God, yet it is not right, with regard to him, to regard among evils that punishment which he justly inflicts. Plato, indeed, was ignorant; but James, leaving to God his right and office of punishing, only removes blame from him. This passage teaches us, that we ought to be so affected by God's innumerable blessings, which we daily receive from his hand, as to think of nothing but of his glory; and that we should abhor whatever comes to our mind, or is suggested by others, which is not compatible with his praise. God is called the Father of lights, as possessing all excellency and the highest dignity. And when he immediately adds, that there is in him no shadow of turning, he continues the metaphor; so that we may not measure the brightness of God by the irradiation of the sun which appears to us. [1]

Footnotes

1 - This verse must be taken in connection with what as gone before. When he mentions "every good gift," it is in opposition to the evil of which he says God is not the author. See Matthew 7:11. And "every perfect free-gift," as dorema means, has a reference to the correction of the evil which arises from man himself. And he calls free-gift perfect, because it has no mixture of evil, what he throughout denies that God is the author of. Then the latter part of the verse bears a correspondence with the first. He calls God "the Father of Lights." Light in the language of scripture means especially two things, the light of truth, divine knowledge and holiness. God is the father, the parent, the origin, the source of these lights. Hence from him descends every good, useful, necessary gift, to deliver men from evil, from ignorance and delusion, and every perfect free-gift to free men from their evil lusts, and to render them holy and happy. And to shew that God is ever the same, he adds, "with whom there is no variableness or the shadow (or shade, of the slightest appearance) of a change;" that is, who never varies in his dealings with men, and shews no symptom of any change, being the author and giver of all good, and the author of no evil, that is, of no sin.

Do not err, my beloved brethren - This is said as if there were great danger of error in the point under consideration. The point on which he would guard them, seems to have been in respect to the opinion that God was the author of sin, and that the evils in the world are to be traced to him. There was great danger that they would embrace that opinion, for experience has shown that it is a danger into which men are always prone to fall. Some of the sources of this danger have been already alluded to. Notes, James 1:13. To meet the danger he says that, so far is it from being true that God is the source of evil, he is in fact the author of all that is good: every good gift, and every perfect gift James 1:17, is from him, James 1:18.

Do not err - By supposing that God is the author of sin, or that he impels any man to commit it.

(13) Do not err, my beloved brethren.
(13) Another reason taken from opposites: God is the author of all goodness, and so, since he is always like himself; how then can he be thought to be the author of evil?

Do not err, my beloved brethren. For to make God the author of sin, or to charge him with being concerned in temptation to sin, is a very great error, a fundamental one, which strikes at the nature and being of God, and at the perfection of his holiness: it is a denying of him, and is one of those damnable errors and heresies, which bring upon men swift destruction; and therefore to be guarded against, rejected, and abhorred by all that profess any regard unto him, his name and glory.

Do not err in attributing to God temptation to evil; nay (as he proceeds to show), "every good," all that is good on earth, comes from God.

Do not err. Either about the source of sin or of all good gifts.
Every good gift, etc. All gifts that truly bless us are God's gifts.
Father of lights. God, the Creator of every light of the material world, and the source of all moral light.
No variableness, etc. God is unchangeable, always the same, nor does he cast a shadow of turning like the sun. The allusion is to the constantly changing shadows of objects in the sunlight caused by the movement, not of the sun, but of the earth.
Of his own will begat he us. Not in caprice, but our birth as children of God was due to his eternal will.
Kind of first fruits. The early converts are often called first fruits of the gospel.

Do not err - It is a grievous error to ascribe the evil and not the good which we receive to God.