From “Early Christianity And Edessan Culture”, chapter 6 of Steven K. Ross’ Roman Edessa, a nice summation of Gnosticism which highlights its Neoplatonic influence;
Gnosticism (or ‘Gnosis’) as a philosophy remains ill defined, as is to be expected of an esoteric movement that, until the discovery in this century of a secret cache of texts, was known primarily through the writings of its detractors. Although it is misleading to speak of a unitary ‘Gnostic religion’, it can in general be said that the Gnostics stressed salvation from the evils of existence but de-emphasized both ‘faith’ and moral behaviour, or good works, as paths to it, putting their trust instead in insight, or the knowledge of certain mysteries known to an elect few who would uniquely be saved. Along with this soteriology went a dualistic cosmology and theology that, like Marcion (himself often counted among the Gnostics), tended to deprecate the world and even the heavenly bodies as the work of an inferior Demiurge. The Gnostics spoke instead of an invisible or ‘stranger’ God, indescribable and in the unseen heaven, as the true source of all good, and the one with which the adherents of gnosis – trapped in a world of darkness and matter – must strive to be reunited.
For the Gnostics, salvation came through escaping Plato’s metaphorical cave, where they had been mistakenly imprisoned by a lesser, clumsy God.