For many deceivers have gone out into the world, those who do not confess the coming of Jesus Christ in the flesh. Such a one is the deceiver and the antichrist.
2 John 1:7 (ESV)
What is the most essential doctrine in Christianity? You might argue with Paul that it is the crucifixion and resurrection of Jesus (1 Cor. 15:3-5). Or you might side with John that it is confessing that Jesus Christ has come in the flesh. But these are two sides of the same coin. Paul points to the work of Jesus, while John emphasizes the person of Jesus. Who Jesus is and what he did are at the heart of the Christian faith.
John appears to be arguing against Docetism, an early heresy claiming that Jesus only appeared to be human. That he did not have an actual human body and did not suffer on the cross. His birth, death, and resurrection were merely an illusion.
John makes what he thinks about Docetism clear. Those who claim that Jesus was not a real human are deceivers. And, even worse, they are antichrists. Those who hold to that teaching are not true believers. He goes on to claim that they do not have God (1 John 1:9). And he warns his readers to have nothing to do with them lest they share in their “wicked works” (1 John 1:10).
Jesus Is Fully Human
The church grappled with understanding the nature of Jesus as fully God and fully human, and with the triune nature of God, in its first few centuries. These are not easy concepts to understand. During this time, several alternatives were proposed and discussed. Most of these were discarded as heretical. The Nicene-Constantinople Creed was ultimately produced to define the orthodox position of the church concerning these key doctrines.
Today, the church is divided into many different traditions, each with its own doctrinal statements and polity. But, at the core of all orthodox traditions is this common belief in the nature and work of Jesus and the nature of the triune God. Including the doctrine of the incarnation of Jesus. Those who deny Jesus as the Son of God (1 John 1:3) who became human are, according to John, antichrists.
