The universal truth
When I had my most intensive period of reading Zen, Taoist and Buddhist literature a couple of years ago, I frequently felt that there must be some universal truth that unites all religions and philosophies, although it is expressed using different vocabularies.
When I searched Amazon for The Doors of Perception I found another book by Huxley that seems to be about this commonality of religions: The Perennial Philosophy. I’ve added it to my want-to-read list.