John Calvin on James 1:16

16 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.