I was skeptical about this book for two reason. When something is trendy, like the Enneagram, I hate it by default. (The first version of this book, to be fair, was from the 1980s.) I’ve also done a lot of introspective exercises in the last few years, and at this point I’m a bit skeptical of more of it.The reason is, at some point I think you have to focus less on yourself and more on the rest of the cosmos. I was mentally primed to not finish this book. About halfway through, though, it was obvious this would be a five-star review. Like my other five-star reviewed books, this one changed me by making think about the world in a new way. 
If you haven’t heard of the Enneagram before, you can think of it as kind of an ancient Meyers Briggs Type Indicator, mixed with a little religious mysticism and Hippocrates’ four humors. The Enneagram is kind of like a clock face, only it contains nine numbers instead of 12 numbers. There are nine related Enneagram personality types, and each type provides insight on a different flavor of person. Each flavor has its own strengths, weaknesses, and motivations. While these kinds of tests are systems aren’t new, the authors trace the Enneagram (in various forms), back to Sufi, Christian, and Kabbalah roots.
If things ended there, this book would be less interesting. What is most useful in the Enneagram is the connection between the types (see the cover for an idea of the connections). Understanding the connections helps you understand how you can grow as a person for the better and flourish. It can also help you better understand your spouse, your friends, your parents, and your kids.
Another benefit of the book is that the authors break down each type by characteristics, motivation, Biblical examples (the authors are Franciscan and Lutheran), Scripture, symbolic animal/color/country, and more. As mentioned above, the book helps you understanding the healthy and unhealthy versions of each type. It uses the more “churchy” terms of “unredeemed” and “transformed”.
I can understand why someone would be skeptical of the book, either because the Enneagram is trendy or because this particular book has a religious focus. You may prefer visiting The Enneagram Institute website for more secular information, but I do think this particular book is pretty respectful of lots of schools of thought.