Searching for God knows What by Donald Miller

As I quite enjoyed listening to Donald Miller audiobook "Million miles in a thousand years" I thought I would check out some other of his books. I always enjoyed Miller's humor which brought in some deep thoughts as well.

While I was in London I had a chance to start reading Blue like Jazz, which is more about his search for truth and finding it, as Miller says, Christian spirituality. I was wondering why he didn't just say Christianity, but I guess that might be to broad and even have negative connotations when compared with some people in christian circles.