1 John 4:2 Hereby know ye the Spirit of God: Every spirit that confesseth that Jesus Christ is come in the flesh is of God:
3 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.
Failing to confess that Jesus Christ came in the flesh has NOTHING to do with recognizing that Christ died on the cross in a tableau in 33 AD.
Failing to recognize that Christ came in the flesh has EVERYTHING to do with the incarnation of the God man.
This is the point God makes in the opening chapter of John:
John 1:1 In the beginning was the Word, and the Word was with God, and the Word was God.
14 And the Word was made flesh, and dwelt among us,...
Yet despite God stating clearly that the Word was God and that the Word (God) was made flesh---we have all kinds of erroneous gospels (Jehovah's Witnesses, Mormons, etc) that refuse to acknowledge that Jesus Christ was Almighty God in the flesh.
All those other kind of gospels that fail to refuse the wonderful Bible truth that God became flesh (man) are of the spirit of anti-Christ and are certainly not of God.