"Fasting" is about biblical fasting - what it is, what it is not, what it it entails, and what it was in the past. Part 1 gives descriptions of 9 different types of fasting, and Part 2 gets into more of the practical aspects of fasting. The first part is considerably lengthier than the second part and goes into great detail of the different types of fasting he describes. McKnight's whole premise in the book is a formula for fasting: A (sacred moment) → B (fasting) → C (results). "A" is a sacred moment in a person's life that leads to "B" (fasting), which produces "C" (results).
I understood McKnight's formula, which I believe he explains well, but there were other phrases he used that were unfamiliar and not very well explained (or weren't explained until much later), phrases that he seemed to make up and aren't used outside of his book. I found that this made it difficult to stay connected to the book.
His descriptions of the different types of fasting (each given its own chapter) felt stretched at times. It seemed to me that some of the chapters could have been combined because they were so similar, which made it difficult to create a distinction between them. However, I think that McKnight does a great job of explaining that fasting isn't one-dimensional, that there are different reasons for fasting and different aspects to it.
I didn't always agree with McKnight, but overall I thought he did a decent job of explaining fasting historically, biblically, and practically, especially for a subject that doesn't have much written on it. I especially think that his formula is concise and understandable. This is a book I would recommend to those who are looking for a basic, short summary/history of fasting.