1 John 4:1-3

1Beloved, do not believe every spirit [speaking through a self-proclaimed prophet]; instead test the spirits to see whether they are from God, because many false prophets and teachers have gone out into the world.

2By this you know and recognize the Spirit of God: every spirit that acknowledges and confesses [the fact] that Jesus Christ has [actually] come in the flesh [as a man] is from God [God is its source];

3and every spirit that does not confess Jesus [acknowledging that He has come in the flesh, but would deny any of the Son’s true nature] is not of God; this is the spirit of the antichrist, which you have heard is coming, and is now already in the world.