Second time through, still an incredible resource. Having my students start with this.
First read:
This book was, without question, the best book on Dietrich Bonhoeffer I have read to date. The first half of the book is a biography of Bonhoeffer's life. I've read two other Bonhoeffer biographies that are a few hundred pages each, and this one was much more enjoyable for a "casual Bonhoeffer reader." If you are looking to know every single detail of his life, I would recommend Charles Marsh's "Strange Glory." (I haven't read Bethge's definitive biography yet). However, if you are looking for an overview of Bonhoeffer's life that really pinpoints the overarching story of his life and will give you a good grasp on why he is still such a popular theologian to be researched and read, this book is your best bet.
What's brilliant about this book is that it is not only a very well written short biography, but it also condenses volumes upon volumes of Bonhoeffer's theological work into a few chapters. (The book is only 150 pages long). The major themes in Bonhoeffer's works are: Christ existing as community, costly grace, vicarious representative action/ ethics as formation, and religionless Christianity in a world come of age. There is a chapter devoted to each of these themes that show up throughout his work. Every chapter was fairly easy to grasp and as a result I feel like I know much more about Bonhoeffer than before I read it.
If someone came to me saying that they wanted to know more about Bonhoeffer, I would recommend this book first. I can't think of higher praise for it.