“I say this because many deceivers have gone out into the world. They deny that Jesus Christ came in a real body. Such a person is a deceiver and an antichrist.”
2 John 7 NLT
A doctrine that we call today incipient gnosticism inserted itself into the first-century church. It was resisted with great force by the apostles and inspired teachers.
Many if not most false doctrines today trace back to wrong ideas about God, Christ, or the Holy Spirit. They ought to be identified and rejected soundly.