2nd Century BCE+: Mithraism and Christianity1st Century: The Ebionites
Jewish Christianity - the OT laws must be upheld1st-7th Century: Gnosticism
The inferior OT god is subverted by the True God1st-14th Century: Adoptionism
Jesus was only human until his baptism1st-7th Century: Docetism
Christ only appeared human but was divine2nd-8th Century: Arianism
The Father is Greater than the Son2nd-5th Century: Marcionites
Jesus came to overthrow fake God of the OT4th Century: The rise of modern Christianity
Cappadocian, Nicene, Pauline and Trinitarian Christianity
“Docetism and its various branches held that Christ's human body was merely a phantom, and that his suffering and death were but appearance. If he suffered, he was not God, they argued, if he was God, he did not suffer: a most reasonable conclusion.”
Some of the earliest groups of Christians were docetist but after the rise of Cappadocian and Pauline Christianity they were forcibly silenced and mostly eradicated. They believed that Jesus was a purely spiritual projection, sent by God to inform and lead. Joseph didn't impregnate Mary because Jesus didn't come from any physical seed; Mary conceived him to fulfil prophecy. Jesus couldn't have been physical because the physical world was fallen, imperfect and separate from god - in this docetist and gnostic Christians agreed. The reason Jesus didn't write anything himself or baptise anyone (John 4:1-2) is because he was a phantasm and could not. St Paul wrote that the Son came "in the likeness of flesh" (Romans 8:3).
The first belief amongst Christians was that of adoptionism, which is related to docetism. Some docetists had adoptionists beliefs: instead of Jesus always being a projection of God, at his baptism Jesus the human was endowed with Christ, the messiah. This is why no amazing stories exist of Jesus as an infant, teenager or young adult. No cult of followers formed around him, and none of the Hebrew scribes mention him amongst their lists of magicians and wonder-workers. Jesus was a normal human; hence why the genealogies in the gospel trace his lineage to Joseph, his natural father. The spirit of God descended upon him in the form of a dove (Matthew 3:16, Mark 1:9-10 and Luke 3:22) which is why in John 1:32-34 God declares that he has (now) chosen Jesus. Because the Christ was eternal god and could not die, he departed from Jesus when he was hung on the cross. At that point, as recorded by Mark 15:34, Jesus cried out "My God, my God, why have you forsaken me?". Or literally translated "Why have you left me behind?"2.
The Gospel of Peter was perhaps even more widely read by the first Christians than the Gospel of Mark3. In verses 10-20 it is specifically noted that Jesus hung on the cross silently "as if he had no pain" until the time that the Christ left him, at which point he cries out "My power, O power, you have left me" and is then "taken up", however, his body remains on the cross. In the now found Gospel of Judas, Jesus would often be seen with completely different physical forms. "Often he did not appear to his disciples as himself, but he was found among them as a child" (33:19-20). [...] Jesus is able to change his appearance at will, according to this text - an idea found in a number of other early Christian writings [... including] the Acts of John". The Acts of John is a gnostic text, not from Nag Hammadi and in one story in it, one disciple sees Jesus as a child while at the same time another sees a cheerful man, and then as a man with a thick beard. From a docetist point of view, this makes sense, as the spirit of Christ is a phantom-like projection, so could of course appear however he wanted to appear4.
So how did modern Trinitarian Christianity begin? See: "How Modern Christianity Began: The Cappadocian-Nicene-Pauline Roman Amalgamation" by Vexen Crabtree (2008)
These early beliefs seem so at odds with modern Christian ideas about the Trinity simply because the idea of the Trinity itself had not been thought of. As Christianity emerged as a fusion of different historical religious styles and beliefs, there were growing arguments over exactly what form Jesus would have taken, or did take. The phrase "Jesus incarnate" came about specifically so that non-docetist Christians could differentiate themselves from the docetist kind.
Docetism was popular enough amongst Christians that multiple authors and Church Fathers wrote arguments against them. The author of the Gospel of John specifically went out of its way to awkwardly state that "the Word became flesh, and dwelt among us" (John 1:1,14). Other anonymous letters and texts which accepted the Gospel of John were later named after John and the resulting literature called Johannine texts. 1 John 4:2-3 says that you can only be godly if you confess that Jesus was physical - docetists, says 1 John, are of the antichrist. Another Christian wrote against docetism in the name of John, and also said that docetists were ungodly. Despite being a forgery, the letter became known as the Second Epistle of John (2 John) and was also canonized in the New Testament, no doubt because the Cappadocian/Nicene Christians found it so useful to back up their belief in a physical fully-God and fully-Human Jesus.
Christian theologians Ignatius of Antioch (died between 98 and 117CE), Irenaeus (115-190CE), and Hippolatus (170-235CE) wrote against the error in the first few centuries5. Around 197-203CE the Bishop of Serapion of Antioch wrote against docetism after finding it in Rhosus, specifically, he wrote against the Gospel of Peter in a tract he titled "The So-Called Gospel of Peter" pointing out that although it was mostly correct, the Gospel of Peter could not be used because it supported docetism.6. St. Jerome (died 420CE) complained that "while the apostles were still surviving... the Lord's body was asserted to be but a phantasm"7. In 451CE, the great Christian Council of Chalcedon also condemned docetism5. Even though the orthodox hunted down and tried to eradicate heretics with increasing violence, the use of the Gospel of Peter continued until at least the 6th/7th century8 by which time the physical and literary dominance of Pauline / Nicene Christianity had become so great, it was getting very hard to imagine Jesus in any other way but theirs.
“The Second Epistle of John (2 John) is very short, just 13 verses. The author writes using the name of a well respected Christian in order to convince others that a particular belief is wrong. The entire epistle is about this one point. He writes against the belief that Jesus' body was spiritual in nature, and not fleshy; a belief known as docetism.”
The Bible (NIV). The NIV is the best translation for accuracy whilst maintaining readability. Multiple authors, a compendium of multiple previously published books. I prefer to take quotes from the NIV but where I quote the Bible en masse I must quote from the KJV because it is not copyrighted, whilst the NIV is. [Book Review]
(1993) Jesus Versus Christianity. Originally published 1988. Cambridge International Publishers, London UK.