James 2:19 "You believe that God is one. You do well; the demons also believe, and shudder."
Then thirdly, true saving faith is fruitful. James' whole point in his discussion in James 2 is that the one who possess true saving faith will bear fruit. Jesus notes in Matthew 7:16-19 "You will know them by their fruits. Grapes are not gathered from thorn bushes nor figs from thistles, are they? 17 So every good tree bears good fruit, but the bad tree bears bad fruit. 18 A good tree cannot produce bad fruit, nor can a bad tree produce good fruit. 19 Every tree that does not bear good fruit is cut down and thrown into the fire. 20 So then, you will know them by their fruits."