Sandras's thesis is that far too many Christians are stuck in what he terms "spiritual suburbia." It's pretty on the outside, hollow in the inside. We settle for less than what God intends, often ignoring our calling and getting too involved in things that seem helpful and holy, but ultimately don't bring us closer to God.
It was an interesting read, full of many insightful stories and ideas. It's a good "afflicting the comfortable" type of book, holding a mirror up to contemporary Christian society and urging them to search for a deeper relationship with God.
My one complaint is that while Sandras identifies many problems, he doesn't offer many solutions. He makes a few suggestions how to change one's faith but nothing that seems to go too deep. That's not exactly helpful, especially with a book like this. A reader might see how hollow their faith is but then have little to no idea how to "fix" things. Given how short the book is, Sandras probably could have included a little more material.