There are two insidious nothions, from the point of view of Christianity in the modern world. (No doubt ther eare more than two, but the others will have to wait.) One is that religion and religious experience are illusions of some sort (Feuerbach, Freud, etc.), and the other is that religion itself is real, but your belief that you participate in it is an illusion. I think the second of these is the more insidious, because it is religious experience above all that authenticates religion, for the purposes of the individual believer.

-Marilynne Robinson, Gilead (pg. 145)