SOURCE: W. W. Wiersbe
It comes as a shock to people that demons have faith!
What do they believe?
For one thing, they believe in the existence of God; they are neither atheists nor agnostics. They also believe in the deity of Christ. Whenever they met Christ when He was on earth, they bore witness to His sonship (Mark 3:11–12). They believe in the existence of a place of punishment (Luke 8:31); and they also recognize Jesus Christ as the Judge (Mark 5:1–13). They submit to the power of His Word.
“Hear, O Israel! The Lord our God is one Lord!” (Deut. 6:4) This was the daily affirmation of faith of the godly Jew. “You believe that there is one God. Good! Even the demons believe that—and shudder” (James 2:19, NIV).
The man with dead faith was touched only in his intellect; but the demons are touched also in their emotions. They believe and tremble.
Wiersbe, W. W. (1996). The Bible exposition commentary (Jas 2:18). Wheaton, Ill.: Victor Books.