1 John 4:1-3
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. By this you know the Spirit of God: every spirit which confesses that Jesus Christ has come in the flesh is of God, 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.
It is a fascinating fact that while most modern skeptics have trouble believing Jesus is God, most ancient ones had a hard time believing he was human. This problem of incredulity concerning the ability God and humanity to join in Christ is still with us today. The materialist believes there’s nothing but matter. The New Age gnostic thinks there’s nothing but spirit. But the Word became flesh and showed them both wrong.