What should we do with the kids … ?
Gnosticism is the result of thinking like a Greek and then re-moulding Christianity accordingly. This is implied by the name itself, gnosis being the Greek word for "knowledge". Gnostics through history have been puffed-up individuals, just like Simon Magus, who have boasted "secret knowledge", who consider themselves as special superior beings who, through these divine secrets have ascended to a higher level than mere mortals. The problem comes when others also believe that there is value in following these deluded individuals. We will read more of this later on.
Just like Marcionism already mentioned, Gnosticism was borne from the dualism of Plato. Remember Plato's major statement: the spiritual world is good, the material, physical world is bad. Because of this, Gnostics (as with Marcion) believe that the material world was created by a "lesser god" and that Jesus, the "greater god" taught secret knowledge to the "spiritual elite". Gnostics have always been great scribblers and a lot of their early writings have been found, which is a shame!
These were the type of people faced by Justin Martyr, or Justin Apologist, who wrote a series of letters, the apologies, to fight these ideas. Yet he wasn't the "main man" of the early Church; the greatest apologist of that period was Irenaeus, the Bishop of Lyons, a disciple of Polycarp.
Irenaeus' best known book was Against Heresies, which did what it said on the tin. It's main target was Gnosticism, particularly that practiced by a guy known as Valentinus, the best known Gnostic heretic of the 2nd Century AD. Although Valentinus had a large following and wrote much, little of his writings survive. His teachings were classic Gnosticism, mixing teachings from the apostles with the dualism of Plato and ending up with an esoteric system suitable only for the "superior intellects" of the day. Ireneaus dealt with Valentinus' teachings in Against Heresies using humour and ridicule. He lampooned his version of Gnosticism in a satire involving guords, cucumbers and melons.
Docetism was another form of Gnosticism dealt with by Ireneaus. Another dualistic twist, this heresy may seem ridiculous to us, but it was a serious problem at that time. Docetists could not believe that the "spiritual" Jesus could have suffered, wept, hungered, thirsted and died in agony. Consequently, they declared that Jesus only appeared to experience these things. This of course is an extreme consequence of dualism and it required them to actually change the verifiable facts of Jesus' life on Earth in order to fit in with their philosophy.
Ireneaus had yet another target in his cross-hairs; a heretic called Montanus. Here was a Christian who "heard voices", claiming them as direct revelations from God and usually travelled around with two women of similar inclinations, one of whom claimed that Jesus had appeared to her in female form. Known as The Three, this sorry band created havoc throughout the Christian world of the mid-2nd century AD. They spoke to large gatherings, driving sensible folk into ecstatic excitements on hilltops, waiting for the Second Coming. Perhaps you can see parallels to some streams of the Church in the 21st century?
Irenaeus knew that this sort of nonsense had to be dealt with otherwise all sorts of misguided individuals were going to start hearing voices and deceiving the masses. He declared that the best way to put a check on these people was to turn to Holy Scripture as authority. The main problem was that the New Testament had not been fully compiled yet, although obviously all the letters and gospels had been doing the rounds of the churches of that day. Irenaeus was instrumental in protecting the early Church from people like Marcion, who were distorting the Word of God, and folk like Montanus, who were trying to add to it!
(This is an abridged extract from Steve's book How the Church Lost the Truth: And How it Can Find it Again)