The book outlines seven concepts for effective communication. They are explored through the story of an imaginary preacher searching for a new way to engage his congregation. In fact the book falls into two parts, the story and the explanation. It's almost like a parable and a commentary (now where have I seen that pattern before...).
Whether or not you agree with the idea of the one point sermon, I think you will find a lot of helpful insights into the communication process of preaching. For a long time now I've been working with the idea in the back of my mind that preaching is less and less about transmitting information and more and more about inspiring change. I'm not sure I'm very good at that, but maybe some of the lessons I've learned form reading this book will help me to do better.
If you're new to preaching, I think you will find this book exceptionally helpful, but that will depend upon your goal. If you've been preaching for years, then it might just be time for a fresh look at what you've been doing all that time.
Possibly the most challenging aspect of the book is the challenge to preach from memory. Not something may colleges and older preachers would probably advocate but not quite as drastic as it sounds, the authors impress upon the would-be communicator that the message must be internalised by the speaker. My notes have got longer over the years to help me make sure I say what I intend to say. I was always prone to tangents and more precise notes help me avoid that trap.
But I agree that the core of the message must be in me if I want it to get in the congregation. To paraphrase the book, how can you expect anyone else to remember what you say if you can't remember it?