Another book I can't find a good link to, but this review is not really to recommend this book. It is to recommend reading a book similar to it.
Like it or not statistics say that the overwhelming majority of humanity consider themselves religious. A huge percentage of them subscribe to a handful of "Great" faiths, Buddhism, Confucianism, Taoism, Judaism, Islam and Christianity. Many other subscribe to folk, animist, and other religions.
If you would like to understand the mind of humanity, what drives it in so much of its day, I'm not sure you can do so without at least a basic understanding of the religions which they follow. Humans created religion for a reason, they follow religion in their billions for a reason, they live, die and kill for their religions, it is worth trying to ascertain what those reasons are.
If you would understand the world, you should read a book like this.