Gnosticism is a blanket term for various religions and sects most prominent in the first few centuries A.D. Its name comes from the Greek word for knowledge, gnosis, refering to the idea that there is special, hidden knowledge that only a few may posses. The occult nature of Gnostic teaching and the fact that much of the evidence for that teaching comes from attacks by orthodox Christians makes it difficult to be precise about the differences between different Gnostic systems.
Gnosticism taught generally that matter was evil, and was the creation of a lesser god (called the demiurge, after Plato). But human bodies, although their matter is evil, contained within them a divine spark that fell from the good, true God. Knowledge (gnosis) enables the divine spark to return to the true God from whence it came.
Many Gnostics (especially the followers of Valentinius) taught that there was the One, the original, unknowable God; and then from the One emanated Aeons, pairs of lesser beings in sequence. The Aeons together made up the Pleroma, or fulness, of God. The lowest of these pairs were Sophia ("Wisdom," in Greek) and Christ. Sophia sinned by seeking to know the unknowable One, and as a consequence of her sin the Demiurge came into being, who created the physical world. Christ was then sent to earth to give men the gnosis needed to rescue themselves from the physical world and return to spiritual world.
Gnostics identified the Demiurge with the God of the Old Testament; thus they rejected the Old Testament and Judaism, and often celebrated those who were rejected by the Old Testament God, such as the serpent, Cain, Esau, etc. Some Gnostics were believed to identify the demiurge with Satan, a belief which contributed to the suspicion with which many Christians regarded them.
Some Gnostic sects were Christians who embraced mystical theories of the true nature of Jesus and/or the Christ which were out of step with the teachings of orthodox Christian faith. For example, Gnostics generally taught docetism, the belief that Jesus did not have a physical body, but rather his apparent physical body was an illusion, and hence his crucifixion was not bodily.
Most Gnostics practiced celibacy and asceticism, on the grounds that the pleasures of the flesh were evil; a few however practiced libertinism, arguing that since the body was evil they should defile it. This led to further distrust, and was an accusation leveled against other groups who did not follow this practice.
Gnostic sects included the Valentinians, the Ophites (so-named because they worshiped the serpent of Genesis as the bestower of knowledge). Marcion of Sinope and Simon Magus both had Gnostic tendencies, but they were not completely Gnostics.
We have two main historical sources for information on Gnosticism: attacks on Gnosticism by orthodox Christians, and extant Gnostic works.
Neither of these two sources is entirely satisfactory. Attacks on Gnosticism by orthdox Christians, hostile as they are, most likely suffer from some degree of bias; and orthodox Christians had a tendency to conflate together the many differing groups opposed to them.
Many Gnostics scriptures and other works were written, but until the late 19th and the 20th centuries, none of them were available, except in isolated quotations in the writings of their opponents. Many 19th century scholars devoted considerable effort to collecting the scattered references in the works of opponents and reassembling the Gnostic materials.
Several finds of manuscripts have been made since, most importantly the Nag Hammadi codices. But though we now possess a reasonable collection of Gnostic texts, they are still often difficult to interpret, due to the esoteric nature of Gnostic teaching. We are also faced with difficulties in identifying which teachers or sects authored which texts.
Origins of Gnosticism
The origins of Gnosticism are a subject of dispute amongst scholars: some think Gnosticism is fundamentally pagan in origin, but has adopted a Christian veneer; others trace its origin to Judaism; yet others think it derives from Jesus, and is a development of his teaching at least as valid as the orthodox one.
Gnosticism in Modern Times
Gnosticism has seen something of a resurgence in popular culture in recent years.
See also: Apocrypha
Pagels, Elaine. The Gnostic Gospels. ISBN: 0679724532