If you're looking to know in advance what this book is about, it is more important to know the subtitle: "Exploring the Views of Ellen White and the Adventist Pioneers Regarding the Trinity".
This book is very Seventh-Day Adventist with the first 5 chapters talking extensively about the history of Adventists and the Trinity doctrine.
I would say, though, that in the last 5 chapters, the discussion becomes more generic to all Christians as Gibson attempts to argue for what he calls "Covenantal Trinitarianism" in opposition to those who are "Anti-Trinitarian".
Besides being a SDA myself, who loves history, I enjoyed this book a lot. Gibson, in the 2nd half of the book, makes some very compelling arguments that I had not thought of before, and even if he's wrong, I found his arguments beneficial and compelling, so worth my time.