1 John 4: 1 - 6
1 Beloved, do not believe every spirit, but test the spirits to see whether they are of God; for many false prophets have gone out into the world.
2 By this you know the Spirit of God: every spirit which confesses that Jesus Christ has come in the flesh is of God,
3 and every spirit which does not confess Jesus is not of God. This is the spirit of antichrist, of which you heard that it was coming, and now it is in the world already.
4 Little children, you are of God, and have overcome them; for he who is in you is greater than he who is in the world.
5 They are of the world, therefore what they say is of the world, and the world listens to them.
6 We are of God. Whoever knows God listens to us, and he who is not of God does not listen to us. By this we know the spirit of truth and the spirit of error.

EWTN