“gnosticism” (from the Greek word “knowledge”).

After the Pauline battle for freedom from the law, Gnosticism was the most dangerous heresy that threatened the early church during the first 3 centuries.

Gnosticism, influenced by such philosophers as Plato, advocated a dualism asserting that matter was inherently evil and spirit was good. As a result of this presupposition, these false teachers, although attributing some form of deity to Christ [they] denied His true humanity…

It also claimed elevated knowledge, a higher truth known only to those in on the deep things. Only the initiated had the mystical knowledge of truth that was higher even than the Scripture.

Instead of divine revelation standing as judge over man’s ideas, man’s ideas judged God’s revelation.

The heresy featured two basic forms. First, some asserted that Jesus’ physical body was not real but only “seemed” to be physical (known as “Docetism” from a Greek word that means “to appear”). John forcefully affirmed the physical reality of Jesus by reminding his readers that he was an eyewitness to Him (“heard,” “seen,” “touched,” “Jesus Christ has come in the flesh”—1:1–4; 4:2–3).

According to early tradition (Irenaeus), another form of this heresy which John may have attacked was led by a man named Cerinthus, who contended that the Christ’s “spirit” descended on the human Jesus at his baptism but left him just before his crucifixion. John wrote that the Jesus who was baptized at the beginning of His ministry was the same person who was crucified on the cross (5:6).

Such heretical views destroy not only the true humanity of Jesus, but also the atonement, for Jesus must not only have been truly God, but also the truly human (and physically real) man who actually suffered and died upon the cross in order to be the acceptable substitutionary sacrifice for sin (cf. Heb 2:14–17). The biblical view of Jesus affirms His complete humanity as well as His full deity.