There is an agnostic sensibility that runs through William James – in this sense: he knows that any claim of knowledge based on religious experience could, in principle, be mistaken.
But it may be true, too. He's convinced that the fruits of "spiritual emotions" are morally helpful for humankind, notwithstanding that some fruits become rotten. He's probed mystical experiences – that sense of oneness with the Absolute – to see whether they can decide the case. They can for the individual concerned, he concludes. But, as he observes at the start of lecture 18, mysticism is "too private (and also too various) in its utterances to be able to claim a universal authority". So, in the final sections of the Varieties, the question of whether religious experiences point to objective truth becomes pressing. "Can philosophy stamp a warrant of veracity upon the religious man's sense of the divine?" he asks.