Gnosticism is generally dualistic. That is, it maintains that reality is found in the interplay of opposites, such as good & evil, spirit & matter, soul & body. For this reason, it often denies the doctrine of creation as that event considers reality to have been created by a totally good God apart from Himself. Gnosticism prefers a more Pantheistic explanation in which reality is the result (synthesis) of the interaction of good & evil. Though much of the Bible may sound dualistic, it is not necessarily so in order to speak of the relationship of spirit & flesh, good & evil. A reaction against this dualism is monism. Monism holds that seeming distinctions are really different faces, perspectives, angles of the One. Here a person sees the "distinctions" in life are really different perceptions of the Unity. (This is a forerunner of Christian Science as symptoms, illness, evil, suffering are illusory & it is only the One of reality which truly exists). Monism is no more right than is gnosticism. Monism, by its overreaction, denies the separateness of distinctions. Evil is denied if God is affirmed. By its denial of creation, thereby ruling out of existence a deistic God, monism thus declares reality illusory. How can it rule out God if it rules out evil by affirming God? Quite simple. God is affirmed formally (subjectively) but not materially (objectively). The being of God is exchanged for the idea of God. The school of Process Theology can be understood in light of Hegel's dialectic here. Man & God are only separated by degrees of realization.
GOD ------------------------------ HUMANITY
As Joseph Smith, the founder of Mormonism once said, "God is what man may be, man is what God once was." The Bible teaches that while God is the author of all reality, it differs significantly from monism in that it holds that this author is personal & has created reality separate from Himself, from nothing, rather than an emination. It agrees with gnostic dualism when it sees the basic dualism within reality, however, it declares that such dualism is not an eternal one, but temporal one.
Gnosticism was one of the earliest heresies faced by the young church in the days that it faced relentless persecutions, before finally being recognized as a valid religion by Constantine in A.D. 313 (that is, in the Western empire, A. D. 329; The Eastern empire wouldn't enjoy that freedom until after the death of the traitorous co-emperor, Licinius in A.D. 323). Gnosticism was preceded by Ebionism which had in turn decended from the Judaizers. The epistles to the Galatians was written to counter such groups. It is often held that the first theologian was Irenaeus (125-202) who penned the 5-volume work, Against Heresies (180-89) or more properly, The Unmasking & Refutation of Falsly So-called Gnosis. Another often considered the 1st theologian was the philosopher turned Christian, Justin Martyr (100-165) whose First Apology dealt with pagan arguments regarding Christianity, as wellas his Dialogue with Trypho the Jew with deals with Jewish ones. However, though Martyr's works were more apologetic in tone, the title of the 1st theologian often falls to Irenaeus. This designation, in no way, infers that his spiritual predecessors were any less instrumental in the journey toward orthodoxy. It will become evident. Just as various pagan theologies threatened to kill the church from without, many heresies threatening to undermine orthodox biblical teachings from within. Thus, just as Solomon declared in Pr. 27:17 "As iron sharpens iron, so one man sharpens another," the early church formed its understanding of orthodox Christian theology by interacting with contemporary heresies,only accepting that which stands up to the scrutiny of scripture (1 Jn. 4:1) since "all scripture is God-breathed & is useful for teaching, rebuking, correcting & training in righteousness." (2 Tim.3:16).
Though many of these Heresies of the Month are contemporaries of the early church, let us not think that they are dead. Certain heresies were condemned only to come before another synod 200 years later to be re-condemned in another form. These heresies can and do re-surface today. The package maybe different but as Solomon wrote in Ecclesiastes "There is nothing new under the sun."