I just finished this book yesterday. This is certainly not some high academic, grit-your-teeth-through-it book. It is written at the average person’s level, very easy to read (I read it in three days without much dedication), and very enjoyable.
The book is about evangelism, but more so, as Mark Dever says in the book’s foreward, “Mack puts the evangel [the Gospel] back in evangelism.” In other words, the main thrust of the book is not directly the idea of sharing the Gospel but understanding the Gospel and then seeing how a precise understanding of the Gospel affects the way you share it. It is an excellent book and the truths within it are surely something, as Christians, we all need to hear and be reminded of constantly. If we think we know the Gospel, we don’t know ourselves. We are inclined to forget the Gospel, neglect the Gospel, de-emphasize the Gospel, add to the Gospel (which in reality subtracts from the Gospel), distort the Gospel, tone down the Gospel, etc. We need reminders such as this.
Here is an excerpt from the last chapter of the book. I believe this portion summarize the main themes rather well.