And every spirit that confesseth not that Jesus Christ is come in the flesh is not of God: and this is that spirit of antichrist, whereof ye have heard that it should come; and even now already is it in the world.
1 John 4:3
There are many that deny Jesus existed. atheist, evolutionist, the false religions of the world, etc. To do so would obviously be to proclaim a spirit of antichrist.
1 John 4:2 KJV Hereby know ye the Spirit of God: Every spirit that confesseth that Jesus Christ is come in the flesh is of God:
1 Corinthians 12:3 KJV Wherefore I give you to understand, that no man speaking by the Spirit of God calleth Jesus accursed: and that no man can say that Jesus is the Lord, but by the Holy Ghost.