I 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.”
When “the Spirit of God” indwells a person He alters the person’s way of thinking and behavior and instills within the person the “substance” and “evidence” (Hebrews 11:1) to know of a certainty that “Jesus Christ is come in the flesh”. The only way a person can know this blessed truth is by inspiration directly from God. When “Simon Peter answered and said, Thou art the Christ, the Son of the living God”; the Lord told him “Blessed art thou, Simon Barjona: for flesh and blood hath not revealed it unto thee, but my Father which is in heaven.” (Matthew 16:16-17). Therefore, it is clear that the only way a person can know “that Jesus Christ is come in the flesh” is for “God”, Himself to reveal it to them. Those who know this blessed truth of “Jesus Christ” are so wonderfully affected by it, that it alters their view of God, of themselves, of life, of death, and the Lord’s Church. This great change also alters their behavior and demeanor so that others can see the effect of “Christ in you, the hope of glory” (Colossians 1:27). Therefore, “Hereby know ye the Spirit of God” is in a person because they confess that “Jesus Christ is come in the flesh”; they confess Him by declaration and by their behavior and works. James put it this way: “I will shew thee my faith by my works” (James 2:18). On the other hand, “every spirit that confesseth not that Jesus Christ is come in the flesh is not of God”; and, if it is not of “God”, then it is of “that spirit of antichrist”! And, the “antichrist” and his vile “antichrists” (I John 2:18) reject “Jesus Christ” and oppose Him and His Word and His Church and His People. It is clear that the “spirit of antichrist” is “even now already … in the world” and is doing his evil, vile deeds.