The earliest of the Gnostic Gospels derive roughly from the same century as the canonical Gospel of John (2nd century CE, which, with its curious introduction and fantastic imagery, was written to read like its competition). "Gnostic" is actually an umbrella term later used to describe a multitude of disparate sects of disparate origin (including Hermeticism; the Nag Hammadi Library contains several tracts considered Hermetic), which were, nevertheless, united by an extent of structural (cosmological, epistemological) themes. Highly syncretistic, two influences predominate: Persian dualistic theology and Greek - specifically Neoplatonic - metaphysics. The Zoroastrian ethical dichotomy has here been transposed upon the Platonic differentiation of substances, the spiritual and the material, to establish a cosmic dualism between these substances and their respective spheres: the intellectual and the visceral. The ubiquitous goal or pedagogy of these systems is to either overcome or master the impulses of the visceral element through a kind of empirical-intuitive knowledge of one's true origin known as gnosis. Greek gnosis is loosely cognate with Hebrew daath, a word significant within Kabbalah, designating, specifically, a kind of sexual knowledge, or a "knowledge of contraries" (also referred to as "acquaintance"). Many of the metaphors employed by the Gnostics - regardless of either an ascetic or libertine commitment — with regard to aeonic emanation (explained in the forthcoming) are of a highly sexual nature; sacraments were sometimes sexual, and certain Christian strains speak of a solution to the temporal dilemma through the reunion of Adam and Eve (the masculine and passive essences of consciousness) within the "bridal chamber" (thalamus, or the "third eye" of the "deathless body").
The theological-cosmological scheme is established as thus: The supreme Godhead consists of a tetrad originating with an ultimately unknowable aeon (Aeons are discarnate beings, similar to the Ideas of Platonism) referred to, alternatively, as Bythos (Depth), Monad (One) or Proarche (First-Cause). It is essentially a deified subconsciousness of the universe. Through a process of emanation (an "out-flowing" of substance) the Bythos androgynously begets a feminine counterpart (This is the Holy Mother, equated with the Holy Ghost of the trinity), and together, through asexual congress, they beget a third (This is sometimes presented as the Christ aeon). This emanationistic process continues until the static Entirety (Pleroma) is formed of these balanced tiers of complimentary aeons; an idea inspired by the Platonic gradation of Forms. There is then a disturbance within the equanimity of the Entirety, usually involving an aeon known as Sophia (Wisdom, worshipped as a Goddess among most Gnostics), which results in the creation of a rogue intelligence. This lesser god, sometimes identified with Yahweh of the Old Testament, begins to create the material sphere by referencing the models of the archetypal world — which it has no thorough cognizance of. Resulting in this act of dissolution, particles of light, once contained within the Entirety, become locked within the kinetic sphere and are retained within materiality through the dynamic of reproduction. The demiurge then proclaims himself to be the only god, and his hubris becomes the model for human selfishness and covetousness.
One sect, known to time as the Sethians (followers of Set, the third son of Adam and Eve) had a particularly colorful account of Genesis. There, the demiurge, a lion-headed serpent known as Yaldaboath (He is also explained as consisting as half Fire and half Darkness: Strife in Ignorance), is roughly comparable to Satan; an evil figure who desires to keep the spirit (the light) of man locked in the cycling of matter through the perpetuation of his ignorance by the power of material obfuscation and the illusion of the self. But while responsible for the creation of man's physical body, he was incapable of supplying him with a spirit. This "spark" of light (or "seed," spermatikos) comes from the Godhead by way of mankind's true creative agent, the Mother Sophia. Hence, man's true genealogy extends back to the Father of All; he is a power consubstantial with God, and greater than the Kosmokrator, whose "cosmos" is a Heraclitean one: actually chaos (The physical world, with all its conflicts and deficiencies, was understood as "the underworld" - Tartarus or Hell - as it was conceived as below the actual sphere of man's origin, the Entirety, or empyrean sphere). Man's salvation depends on the personal cultivation of his gnosis, or the enlightenment bestowed upon him by some heavenly emissary or paraclete. Often, this is the Christ.
Gnosticism offers a Christology not quite docetic; that the Christ aeon is separate from the physical Form of the man Jesus of Nazareth, who was, in this case, an ectypal manifestation of the otherwise immortal Christ. Christ is the syzygy ("yoke") of Sophia, who, as attested Biblically, sits at the Right-Hand of God, which is here the path of the spiritual or intellectual (It is sometimes credited to the aeon Zoe, "spiritual-life"), and could also be considered the path of Form. This identifies Sophia with the Left-Hand; she is therefore a patroness of the Left-Path, or, of the philosophies of the "Left-Hand." This explains her ordeal and her suffering as outlined in the Gnostic account of the Fall; the aforementioned equanimity of the Entirety is disrupted when Sophia became hysterical in her lust for the Father. The empirical, or, better described as "the experiential," is the path of suffering - and suffering is passion (by actual definition). However, the Left-path is also the means of ascension, and so, a common Gnostic aphorism was "The Way Down is the Way Up" - as with a ladder. The intuitive aspect of this process is the revelatory faculty that discloses anything subsisting (hence, a priori) about the world or the self. Gnosis then shares a definition similar to that of an epiphany (which could have meant "light from above"): "a sudden, intuitive perception of or insight into the reality or essential meaning of something, usually initiated by some simple, homely, or commonplace occurrence or experience." For the Gnostics, this type of knowledge demanded an engagement with the world, either for the sake of refuting it, or , perhaps, even to affirm it (The Thomas Gospel features a number of aphorisms that could be considered "life-affirming").
With the actualization of a proper Christian church and an orthodoxy, so-called Gnostics, who offered a view incompatible with the Nicene catechism, were condemned as heretics, excommunicated from the organized church, their elegant doctrines destroyed. Or so it was believed. The books preserved in the Nag Hammadi corpus acquire their name from a collection of multiple codices discovered accidentally in Nag Hammadi, Egypt, in 1945 by two Muslim brothers out to exact a "blood vengeance" on behalf of a deceased relation. Discovering a clay jar while on their itinerary, they were met with initial trepidation for fear that a djinn might reside within the strange vessel. But, considering the potential prospect of gold or jewels, the jar was smashed revealing the bound papyri manuscripts. These manuscripts, written in Greek and Coptic, were unintelligible to the brothers and so the codices bounced around the black market until their serendipitous rediscovery by those with the proper education in understanding their importance.
Prior to the discovery of the Nag Hammadi texts, our knowledge of Gnosticism had been reserved to bias diatribes such as the Against Heresies of Irenaeus. The books contained within the Nag Hammadi library are hugely significant to filling out lacunas within Christian history and to better understanding the transition from polytheism to monotheism. These scriptures also help catalogue a period of Pagan intellectualism when mythology was beginning to be considered for its allegorical-psychological orientation. Gnostic religion provides a monumental milestone between mythology and psychology.