Religion becomes identified in the popular mind with a series of moods, in which the worshipper, disposed therefore by all the arts of the revivalist, relished the flavors of spiritual peace. You needed neither a theology or a liturgy; you did not take the strain of intellectual inquiry, nor associate yourself whole-heartedly with any historic traditon of worship. You floated, safely enough, on the little raft of your own faith, eagerly throwing out lifelines to drowning neighbots as were able to catch it; meanwile the ship was foundering.
There is more to it then that. Gnostics can believe lots of things, but they are all religious Dualists. In Christian form they deny Christs Humanity because Man (in physical form) is uterly evil. Or they deny Christ Divinity for the same reason. They are the first heresy and the most dangerous, because it was founded by the Devil. There can be no denying that, who else would create a system where Good and Evil are equal? All later heresies have some Gnostic aspects to them.