To get back to the topic—
To me, one of the greatest flaws of Gnosticism was its “exclusivity.”
Only CERTAIN people were chosen to understand the esoteric Kingdom of God. The Kingdom of God was not available to everyone, as in the mainstream version. One had to WORK towards perfection through succesive lifetimes.
The God we knew wasn’t even THE God. He was a false God (The Demi-Urge) who ruled the lower “spheres” and was angry and tyrannical, i.e., “The Old Testament God.”
This is what caused the TRUE God (of the higher "spheres above the Demi-Urge), i.e. The New Testament God, to send his Son “invade” the lower “spheres,” thereby proclaiming the TRUE Gospel of the TRUE God in defiance of the FALSE God of the lower realms, thereby hopefully causing a “revolution” of sorts to break out for the “Truth.”
Where do you think Phillip K. Dick got his “Divine Invasions” theme from???
Can anyone say “The Inspiration for THE MATRIX?”
The Gnostic Gospels cannot even agree which of Jesus’s circle were or were not “The Chosen Ones” who were party to the hidden, true knowledge of Jesus. The Gospel Of Thomas says it was Thomas who was the “Chosen One.”
The Gospel of Judas says it was old Iscariot.
The Gospel of Mary says it was…you guessed it. (This is also the Gospel where Jesus is supposed to have "kissed Mary on the…"and the word is lost. Dan Brown enthusiasts got a kick out that one).

uch:
Some Hammadi texts even incorporate Egyptian Hermeticism and old Hermes Trismegistus into the mix.
Personally, a good survey of the motivation behind Gnosticism as a reponse to early mainstream Christianity would have to be (Non-Catholic) Alistair McGrath’s “Heresy” book, which traces a possible reason for it in genuine questions regarding the portrait of God shown in OT and the portrait shown in NT. Good book to read as an alternative to the “poor Gnostics who were persecuted by the Big Bad Orthodox Christians” mainstream narrative you get these days.
Not that there were not persecutions on BOTH sides, but it wasn’t “as simple as that.”
BTW, did you know that Marcion, probably the earliest Gnostic, did not become a Gnostic until AFTER he had been rejected by the Church for trying to deny Christ’s Jewish heritage and to take all Jewish traditions out of the Gospels???
Ultimately Gnosticism is an interesting but unwieldy and inconsistent ideology which, while it proves that early Christianity was NOT monolithic, does nothing to succesfully answer to even refute the Faith ol Old.
And it unfortunately has been used by people wanting to transform Holy Mother Church beyond all reason into something that fits certain political/moral agendas.
Sorry, Publisher you are wrong. And if it comes to pass that Gnosticism supplants Orthodoxy and tradition, I tremble at the fate of Western Civ.