1 John 4:2 By this we know the spirit is of God: every spirit which confesses Jesus Christ in the flesh has come from God,
This verse gives the defensive resource for dealing with false prophets. The central confession of Christianity is that Jesus Christ, the divine Son of God, came in the flesh. What this means has been debated by both orthodox Christians and heretical sects. The central and most basic question one can answer is what to do with Jesus Christ. Are the claims about him in the Bible true, or were they invented by the early church? Are there other revelations about Jesus that add to or supersede the Bible? If Jesus were divine, how could he suffer as a human?
John wrote this letter in part to deal with growing heresies that attempted to redefine the Incarnation. In his Gospel and in this letter, John recounts the perfect balance between Jesus’ divinity and humanity. He truly came in the flesh, but he was also born through the Holy Spirit and came as God’s perfect representation. To look at Jesus was to look at the Father—like Son like Father. Heresy begins when either Jesus’ humanity or divinity is diminished. False prophets distort this balance by either emphasizing his humanity, saying he was only a prophet or lesser “god,” or his divinity, claiming that he was only a spirit or phantom, though quite a convincing one.
The Holy Spirit works in people to lead them to confess that Jesus Christ is Lord (1 Corinthians 12:3). The Holy Spirit brings recognition of Jesus and new life in him. True spirits that come from God agree with the Holy Spirit. The previous verse implies that these spirits are humans or at least work through humans. Behind this verse is the battle that every human faces and that wages behind the scenes in the spiritual world: the battle between good and evil, between what glorifies God and what rejects or distorts God.
This verse points out the difference and determines orthodoxy by recognizing both Jesus’ divinity and humanity. In theological terms, Christology (the study of Christ) determines orthodoxy (true doctrine). Those who teach and preach must equip God’s people to be discerning about what they hear and read. We can be better prepared by knowing the Bible and key theological claims. John expresses his certainty with we know. The best defense against false teaching is to know the True One.