I've only recently started reading the source material and I've learned that the Gnostics believe that the God in the Torah is actually an imperfect God (described as resembling a dragon) and not the true Father of everything. Jesus Christ's father is not the Torah God but the true Father of everything. Jesus Christ was trying to save humanity from the Torah God.
Seems pretty accurate to me. Many people say that jews worship the devil. Well, the Gnostics basically said the same thing in texts over 2000 years old. I've also heard the Torah God is a dragon bit before and thought it was a modern view. I didn't realize it literally was written in texts 2200 years old.
I just find Gnosticism interesting in the sense that it basically discounts the Torah entirely because it suggests the God discussed in the Torah is the imperfect God who isn't really a good God at all and attempts to enslave/entrap humanity. By believing in this Gnostic take, it completely rids Christianity of the Jewish hold on it.
In Gnosticism, it was the imperfect Father who created us but it was an extension of the perfect Father that gave us life. Easily commingled as one Father who gave us both rather than separated out as the Gnostics do.
Demons are mentioned in the original Gnostic text I've been reading but I'd need to delve more into it to truly understand their purpose.
Gnosticism seems to have a different take on demons and demonic possession than most Christians understanding of the two; however, in practice the outcome is similar. Gnosticism suggests there are Archons (rulers of this world) created by the imperfect God who keep humans trapped in this material world. The way in which they keep humans trapped is by distracting humans away from the innate understanding of their divine spark. They do this by distracting humans with vices (so-to-speak) that a Christian would associate with demonic possession and these archons are describes by some as demonic (due to the commingling of religious theories). Gnostics wouldn't just believe in "demonic possession" as a Christian would understand it but they would go on to say it's a defining feature of the material world because it is through demons and demonic possessions the archons keep us trapped in this material world.
Essentially, the Father, the son and the invisible virgin spirit are the trinity in this context.
The resurrection is the reason the Catholic Church declared Gnostics as heretics. The Gnostics believe that Jesus did resurrect but as his true form which is "pure light".