James's gift for distilling the essential ingredients of the religious experience from the great mass of details is evident in every chapter. Taking the approach that extreme manifestations of the religious temperament give us more insight into the subject than the routine features of worship and ritual, he discusses many intriguing accounts of remarkable religious experiences, grouping these experiences into broad types: healthy-mindedness, the sick soul, the divided self and the process of its unification, conversion, saintliness, and mysticism. He also discusses the distinctions between religious experience and philosophy; psychological theories concerning the origin and nature of religious belief; and the overall value of religion to human well-being.
James concludes that religious experience is real insofar as it produces real effects on peoples' lives and characters, and therefore it can and should be the subject of serious scientific inquiry.