Let's review the text from John's first letter that mentions the sign of the antichrist.
1 John 4:2-4 By this you know the Spirit of God: every spirit that confesses that Jesus Christ has come in the flesh is from God; and every spirit that does not confess Jesus is not from God; this is the spirit of the antichrist, of which you have heard that it is coming, and now it is already in the world. You are from God, little children, and have overcome them; because greater is He who is in you than he who is in the world.
John's message is clear: every spirit that acknowledges Jesus, who came in the flesh, as the Christ, is from God. Conversely, any spirit that denies Jesus as the Messiah, despite his human form, is the spirit of the antichrist. This understanding is crucial for our spiritual journey.
The peril that Trinitarians face is not to be underestimated. It's when some of them diminish the humanity of Jesus and inflate his supposed divinity. The Spirit of the antichrist, as John warns, is a spirit that denies the humanity of Jesus, suggesting that a man like Jesus couldn't be the Messiah. This dangerous spirit can seep into the hearts of Trinitarians who unintentionally disregard the humanity of Jesus. We must be vigilant and alert to avoid falling into this trap.
This spirit is evident in the answers to various theological questions such as "Was Jesus actually tempted to sin in the wilderness?" The spirit of the antichrist will say, "No. Jesus couldn't be tempted to sin because he isn't a man, he is divinity." Did Jesus, the man, die for our sins, or did Jesus, the God, die for our sins? The spirit of the antichrist will say that Jesus, the man, didn't die for our sins. It was Jesus the God who died for our sins. Did Jesus the man perform the miracles or did Jesus the God perform the miracles?
You see, Trinitarians run into danger when they are lured into the trap that every significant thing about Jesus was due to his divinity. His manhood is only incidental and insignificant. The allure of the antichrist spirit is to draw us away from the idea that Jesus, having come in the flesh, is the Messiah. Some Trinitarians ostensibly believe that Jesus is 100% man, but when it comes to questions such as those I raised above, they dismiss his humanity when it comes to the significant and important issues surrounding the role of the Messiah.