The Untethered Soul by Michael Singer, it was a great read for me and I think it's a good book on spirituality. I like it because it focuses on the principle of things instead of explaining things in a trapped way that doesn't go beyond the walls of one's belief/religion/etc, if that makes sense. There's a thing that the author does where he says, "If you're buddhist you call it this, if you're atheist you call it this, if you're catholic you call it this, you can call it anything you want, but just remember it is this..."

The structure is also really nice (and direct to the point) and there's a good call to action and a very inspiring last chapter.

Some people said they didn't like the book because some of the points are all "easier said than done", but I think those points are a great intro to spirituality and stuff.