Gnosticism was a trend in the antiquity to combine heretical Judaic mythology with Mesoplatonic concepts. Gnosis according to this original model, was enlightenment of one's own divine nature, usually the inborn ethics and the inborn attitude to the world. When being elected gnostic (on some level) one "married" the heavenly twin in Pleroma, an angel representing the true self. Some Gnostics maintained the monogamous marriage to this perfect twin, some other didn't regard this "monogamy".
The Platonic cosmology claims that there is a perfect eternal world of "Ideas" which is more real than the physical world wherein we live, and in comparison of which this world is just a defect shadow. Mesoplatonism (middle platonism before Plotinus) also borrowed a lot of concepts from the Peripatetics (Aristotle) and the Stoics (Zeno of Citium) and the science of the time, among others Ptolemy's geocentric cosmology of planetary bodies, and the earliest known alchemy. According to the Gnostics and most Platonics, this material world is fundamentally "evil" - so when Plotinos the Neoplatonic attacks the Gnostics for regarding this world as evil, he deviates from the standard Platonic position by adopting the pompous God-powerism shared by Hermetics, Jews and (non-Gnostic) Christians. The "evil" of this world is not the satanic evil from a predator that have selected its victim, or a hateful dictators murderlust against opponents, but rather a fundamentally corrupt quality of the creation that corrupts, decomposes and kills, and that indirectly creates predation and hateful dictators through the action of Error which is kind of a violation against the rules of the divine existences in the World of Ideas or Pleroma. In modern physical terms this "evil" can be compared to entropy. This world inevitably leads to death, and our only way to get eternal life is to emulate the qualities upheld by our heavenly twins who already have eternal life - according to Mani (the founder of Manichaeism) and probably the Valentinians, through the so called Bridal Chamber. Irenaeus reports that some "heretics" admitted through the Bridal Chamber ("nuptial couch" section 3), some through the baptism, and some through incomprehensible formulae. According to the Mandeans a newborn baby will get a secret constellation name (malwasha) to get a connection to the Pleroma above.
The archons, the evil rulers of this world, are a symbol for passions, and strong uncontrolled feelings. Evil rulers affect us and manipulate us through our feelings. Pleroma - the Gnostic counterpart of the Christian Heaven is free from emotions, we are there purely intellectual light beings (page 78) acting perfectly logical according to reason. The Living water (page 89) is a symbol for streams of energy that provides us nourishment in our intellectual form.
Life itself is, according to Gnostic theology, a holy entity (section 2.1.1. Pira), otherwordly and divine, and it turns evil only in contact with the matter, where predation emerges as a mechanism to temporarily avoid death, which in the long run is unavoidable nevertheless, an unchangeable force that drags us down to the center of earth. It is reasonable to imagine Pleroma as a number of Aeons (heavens) of increasing brightness, permanency and purity, but they are full of life that doesn't perish. After the death we have to pass the planets of this Universe, and these are regarded as evil archons keeping us trapped in this world trying to keep us in control astrologically using emotional affect. Mandeans (page 153 and forth) and Ophites are clear with this, and provide secret formulae to pass each planet on our road to Pleroma. This was the established scientific cosmology during the antiquity.