About the book (from Wikipedia):
The Varieties of Religious Experience: A Study in Human Nature is a book by Harvard University psychologist and philosopher William James. It comprises his edited Gifford Lectures on natural theology, which were delivered at the University of Edinburgh in Scotland in 1901 and 1902. The lectures concerned the nature of religion and the neglect of science in the academic study of religion.
Soon after its publication, Varieties entered the Western canon of psychology and philosophy and has remained in print for over a century.
James later developed his philosophy of pragmatism. There are many overlapping ideas in Varieties and his 1907 book, Pragmatism.