The Varieties of Religious Experience by William James

William james was a psychologist long before he was ever a philosopher. He wrote an entire book called the varieties of religious experience where he e dissects basically every type of religious idea that people have ever come up with and tries to find similarities between them. Religion to william james, well, he defines it as man's total reaction upon life. And in that sense, he's far from being tolerant to people just believing in whatever they want.