Nothing is more striking than the secular alteration that goes on in the moral and religious tone of men, as their insight into nature and their social arrangements progressively develop.
 William James, The Varieties of Religious Experience (1902). copy citation

Context

“If disbeliefs can be said to constitute a theology, then the prejudices, instincts, and common sense which I chose as our guides make theological partisans of us whenever they make certain beliefs abhorrent. But such common-sense prejudices and instincts are themselves the fruit of an empirical evolution. Nothing is more striking than the secular alteration that goes on in the moral and religious tone of men, as their insight into nature and their social arrangements progressively develop. After an interval of a few generations the mental climate proves unfavorable to notions of the deity which at an earlier date were perfectly satisfactory: the older gods have fallen below the common secular level, and can no longer be believed in.” source