In this the children of God and the children of the devil are manifest: Whoever does not practice righteousness is not of God, nor is he who does not love his brother.  (1 John 3:10)

By this you know the Spirit of God:  Every spirit that confesses that Jesus Christ has come in the flesh is of God . . . And every spirit that does not confess that Jesus Christ has come in the flesh is not of God.  (1 John 4:2-3)