Docetism – the belief that Christ did not assume a truly human body at his incarnation – was around in the days of the later New Testament writings, as the epistles of John testify.
It was clearly as rather stubborn heresy, for it is also found within the pages of the Qur’an (7th century). According to Sura 4:157-158.
Muslim scholars remained undecided about who they think took Jesus’ place on the cross: with some saying Judas, and others saying some other person. Some have even suggested that Jesus was indeed nailed to the cross, but somehow survived the ordeal.
To the Christian, this denial of the crucifixion demonstrates a tendency within docetic thinking that is also apparent in the teaching of the secessionists referred to in 1 John, viz. that in denying the incarnation of Christ they also must deny the atonement. If Jesus only ‘seemed’ to die for our sins, then our salvation is equally ‘seeming’.