Religion, therefore, as I now ask you arbitrarily to take it, shall mean for us the feelings, acts, and experiences of individual men in their solitude, so far as they apprehend themselves to stand in relation to whatever they may consider the divine. Since the relation may be either moral, physical, or ritual, it is evident that out of religion in the sense in which we take it, theologies, philosophies, and ecclesiastical organizations may secondarily grow.

Lecture II, "Circumscription of the Topic" - The Varieties of Religious Experience (1902)