By this you will know the Spirit of God: If someone claims to be a prophet, John provides a test for them. True prophets and teachers, guided by the Spirit of God, confess that Jesus Christ came in a real body ("in the flesh"). This means they must confirm that Jesus is both fully human and fully God. Those who deny these basic teachings are antichrists (2:18).
Some false teachers in John’s time, called Docetists, taught that Jesus only appeared to have a human body. They denied that God truly became flesh (see 1:1–3; John 1:14).