James 2:19

19Thou believest that there is one God. From this one sentence it appears evident that the whole dispute is not about faith, but of the common knowledge of God, which can no more connect man with God, than the sight of the sun carry him up to heaven; but it is certain that by faith we come nigh to God. Besides, it would be ridiculous were any one to say, that the devils have faith; and James prefers them in this respect to hypocrites. The devil trembles, he says, at the mention of God’s name, because when he acknowledges his own judge he is filled with the fear of him. He then who despises an acknowledged God is much worse.

Thou doest well, is put down for the purpose of extenuating, as though he had said, “It is, forsooth! a great thing to sink down below the devils.” (117)

In the former verse the boaster of mere faith is challenged to prove that his faith is right and therefore saving; the challenger would prove by his works. Then, in this verse, a test is applied — the very first article of faith is mentioned: “Be it that you believe this, yet this faith will not save you: the devils have this faith, and instead of being saved they tremble.