“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

He explains and reveals to us the workings and communications of the spirit of antiChrist which is already in the world.
Every spirit that does not speak in agreement with God that Jesus Christ came in the flesh is not of God; every spirit that sets up another ‘savior of the world’ and markets that savior is not of God, every spirit that does not agree that divinity was manifested in flesh is not of God, every spirit that still denies the workings of divinity in flesh even today, is not of God.
Irrespective of where these thoughts are manifest- folk tale, movies, music, etc. he is telling us that this spirit of antiChrist has infiltrated the world and is pushing the message that divinity did not come in flesh!
They deny and mock your existence as the child of the word of God with the life of God:
“Having a form of godliness, but denying the power thereof: from such turn away.”  2 Timothy 3:5
“For many deceivers are entered into the world, who confess not that Jesus Christ is come in the flesh. This is a deceiver and an antichrist.”  2 John 1:7
Notice the emphasis of the message- Jesus Christ did not come in the flesh; the supernatural does not and can not exist in the flesh- so they deny miracles or the miraculous, they deceive people into exalting psychology and ‘science’ rather than the possibilities of the divine life in Christ.
“O Timothy, keep that which is committed to thy trust, avoiding profane and vain babblings, and oppositions of science falsely so called:”  1 Timothy 6:20
This is the doctrine(teaching) of Christ; that it happened that God came and functioned on this earth as a man expressing divine verities and it is still happening today through every Christian.
“Whosoever transgresseth, and abideth not in the doctrine of Christ, hath not God. He that abideth in the doctrine of Christ, he hath both the Father and the Son.”  2 John 1:9