I listened (on CD?) to quite a bit of The Gnostic Gospels by Elaine Pagels today. I am impressed by how old ideas or themes come up again and again in different guises, so that again and again, people receive the same ideas as if they were completely new. In particular, it seems to me the gnostics were very close in spirit to Transcendentalists -- not that the latter promised such explicit secret revelations as tended to permeate Gnosticism -- but there was a sort of obscurantism or sense of dealing with the ineffable about Transcendentalism which made it opaque to outsiders.
One thing that has always tended to excite people is newness itself, and a variant that I might call "at-last-ness". The perception that an idea or movement is new, or has arrived "at last" tends to give us a certain optimism about it or enthusiasm for it. The "idea whose time has come" is thought to be irresistable or inevitable.
Inevitability is another eternal theme, but is often found tightly bound up with its apparent opposite. We seem strangely happy to view an idea as both "INEVITABLE" and "OVERWHELMINGLY RESISTED". A deep well of folklore supports this strange pairing. Ideas which have been strongly cast in this (dual) light include Monotheism, Enlightenment (with various meanings), the "Triumph of Reason", Equality, Liberty, Democracy.