An antichrist is a deceiver who teaches a false, unbiblical Christ, changing the nature of God to suit their own ends. In the days of the apostle John, one form of deception was Docetism, a Gnostic-Christian belief that Jesus was human, but Christ was a divine spirit that came upon Him at His baptism and left before He suffered and died. Docetists held that physical flesh is tainted and impure, while spirit is pure and holy, thus denying that Christ truly came in the flesh. John warns against ministers who teach such doctrines, identifying them as antichrists who deceive by altering the true nature of Jesus Christ.

Docetism, a misguided notion stemming from Gnostic influences, asserts a false division between the spirit and flesh of Jesus Christ. This erroneous belief posits that Christ was purely a spirit, while Jesus was merely a human vessel, with the spirit of Christ entering and leaving Him as needed, especially fleeing during the crucifixion to avoid association with the physical body. Such a view arises from the Neoplatonic idea that flesh is inherently evil and far removed from God, while spirit is pure and good. Consequently, proponents of Docetism argue that if Jesus had flesh, He would be impure and thus disqualified from being divine. This flawed reasoning attempts to separate the divine nature of Christ from any contamination by a physical body. John directly counters this deception by emphasizing his personal witness to the humanity of Jesus Christ. He saw Him, heard Him, and touched Him, affirming that Jesus was indeed a human being in whom eternal life was manifested for all to see. John further declares that those who possess the Spirit of God must confess that Jesus Christ came as a fleshly human being, a foundational truth of faith. Conversely, those who deny that He came in the flesh are not of God, as such a denial undermines God's plan of redemption. If Jesus Christ were only a spirit and not human, He could not have paid for human sin, for only a human sacrifice could atone for human transgressions. Moreover, John identifies this denial of Christ's humanity as reflective of the spirit of the antichrist, which encompasses any false conception or deceptive teaching about Christ. This spirit is not limited to Docetism but includes any belief that distorts the true nature of Christ, revealing an opposition to Him by promoting an untrue understanding of His identity. Thus, a correct conception of Christ as both human and divine is essential to true faith, distinguishing it from the errors of antichrist teachings.

In his epistles, John addresses the corrupting influence of false teachings, particularly focusing on a gnostic belief known as Docetism. This heresy posited that Jesus was merely a physical man into whom a separate spiritual entity, the Christ, entered at His baptism and departed before His crucifixion. The Gnostics, adhering to Greek philosophical ideas, viewed material things like human flesh as defiled and sinful, while considering the spirit pure. They could not accept that God would come in the flesh or that God could or would die. To them, the concept that the Word became flesh and dwelt among us was nonsense. John counters this by emphasizing that anyone who denies the incarnation of God into human flesh is anti-Christ, opposing the very purpose of the Messiah's life, ministry, and death.