The ancient Gnostics drew a clear line between the material world and the spiritual world of gnosis. Gnosticism is thus dualistic. There is spirit and there is matter. There is the material world and there is the world of the spirit, often called the Pleroma, from a Greek word meaning ‘fullness’ or ‘completeness’. To many, this dualism may initially seem to be surprising, being perceived as a quality that belongs more to a fundamentalist religion than to true spirituality, reminiscent of the importance that many fundamental Churches give to the influence of Satan in this world, which thus turns the world into a moral battleground between Christianity and the forces of evil. But classical Gnostic dualism was a dualism within unity. All and everything springs forth from God, but the material world is a result of the cosmic fall, an error made in the lowest reaches of the spiritual realm.
Matter is the crudest and lowest aspect of the universe, and it is of matter that our bodies are formed. But the creation of mankind could not proceed without a spark of the spiritual realm residing in each human. We humans therefore have a duality of matter and spirit within us. We respond to base matter, but we have divine spirits, in which our true identities reside. Ultimately, everything is contained within the divine, even the base physical world, and it is only in our ignorance (lack of gnosis) that there appears to be duality.
But this world of matter did not come into existence through a mechanical process or by chance. The Gnostics, like the Christians and Jews, thought that the world had been created by God. The Gnostics even agreed that the creator was the same as the God of Christians and Jews. However, the Gnostics felt this God with an arrogant and ignorant abortion, truly a jealous God, a despot who knew nothing of the spiritual realm above him. Thus mainstream religion worshipped the wrong God, and the real God could only be known through gnosis, not through any conventional doctrine or belief.
All of these ideas were expected expressed through the medium of myth, not through philosophy or strict dogma. Gnostic myths come in several flavours, but the mythic framework usually involves a description of the higher realm and an explanation of the fall that occurred, followed by an account of the possibility of salvation and restoration.
– Andrew Philip Smith. (2008. P 5-6.) The Secret History Of The Gnostics. Watkins