It is very likely that gnosticism was born before the Christian era, as we discussed in Part 1. It's possible that some Jewish readers of Greek philosophy, and Plato in particular, were concerned with evil in the world, or the meaning of the universe, and found attractive the precepts of gnosticism over and above the traditions in their sacred texts. Their texts specified that evil comes from Satan–an angelic being, although fallen/evil, under Yahweh's lordship. And their rabbis stressed that evil comes from the "evil inclination" in the heart of man. It's possible that some Jewish readers saw those two options and just didn't find them convincing at all.
It's possible that the "revelation" about the mystery of evil came to these Jewish people as they were reading Plato's Timaeus, where we find the myth of the Demiurge. What was the Demiurge? It was a divine power, but somehow inferior to the one, good God. The Demiurge was responsible for the creation of the universe, which was full of problems and full of evil. In this area is where we find the spark for new revelation. They must have thought to themselves: "If we accept this intermediate divine being, then it would explain how the supreme God, the one and good absolute who is greater than the Demiurge, is in a large part (if not completely) given a pass in the creation of the world. And, therefore, he is free from any fault for the problems in the world and evil. He is ceases to be the explanation for evil in the world."
So, what happened next? The next step in explaining the origin of Jewish and Christian gnosticism is to assume that the Hellenized Jews–those who hypothetically fell captive to the works of Plato –applied Platonic ideas (e.g., the distinction between spirit and matter, the idea of "copies," the immortality of the soul and the division of its parts, etc.) in their own thinking, such as in the reading of Genesis, their favorite book, and the exegesis of its contents.
The starting point for the birth of Gnosticism could be the moment when these Jewish people believed the biblical narrative confirmed what they had read in Plato. The first chapters in Genesis, for example, present creation of Adam in two different accounts. The first came by way of Elohim (literally, "gods") and the second is attributed to Yahweh (i.e., not Elohim; see also Job 1, where the same distinction appears). This convinced these esoteric Jews. They were convinced that the divine revelation itself cryptically made a distinction between a supreme deity (super-transcendent and unreachable) and the actual creator of this wicked world. That would have been where the dualism of the "two powers in the sky"–explained later as the supreme God and the Demiurge–found support. And it was right there using the very Scriptures they had always read.
That was probably the launching pad. From there, according to this hypothesis, these Jewish people also added other religious ideas that were circulating around, focusing their attention on the inevitable struggle between Good and Evil, and the antagonism between the two. This syncretism (i.e., a mixture of ideas from other religious or philosophical views) with those of the Jewish faith ultimately produced a new channel by which one could interpret the message of the Holy Scriptures of Judaism.