Schaff, Philip. History of the Christian Church (The Complete Eight Volumes in One). Amazon Kindle Edition, 2014.
Volume 2, Ante-Nicene Christianity A.D. 100-325, “Chapter 11. The Heresies of the Ante-Nicene Age” Sections 112-136, Loc. 17655-18757.
§ 116. Meaning, Origin and Character of Gnosticism.
Schaff identifies Gnosticism as a “paganizing heresy” and compares it to a form of rationalism (Schaff 2014, Loc. 17915). The basic idea is predicated on the concept of gnosis, a philosophical or religious way of knowing. In the New Testament we find a distinction between true and false gnosis, with the true form coming from faith in God. In contrast, Schaff finds the false version as arrogant and self-conceited (Schaff 2014, Loc. 17922). The Gnostics considered themselves truly spiritual, in contrast to the Christians, who were “mere men of the soul and of the body” (Schaff 2014, Loc. 17922).
During a brief historical summary of Gnosticism, Schaff finds it originating in Greek philosophy but being brought into Christianity at an early time. The tenets largely derive from Plato, though other Greek philosophers can be found (Schaff 2014, Loc. 17938). However, Schaff also finds roots in Babylonian and other Eastern mysticism. It is truly eclectic and syncretistic (Schaff 2014, Loc. 17953).
Because Gnosticism is highly speculative, Schaff considers it inadequate for defining morality (Schaff 2014, Loc. 17968). It resulted in both profligate behavior and severe asceticism, both as outrgrowths of the trivialization of the physical.
Schaff finds a fairly consistent and widespread controversy in Christianity against Gnosticism (Schaff 2014, Loc. 17976). Though it arose to its greatest influence in the second century and largely subsided by the sixth century, the ideas have continued to arise periodically since then.