The reader promise is the practical or emotional value someone can expect from your book. It need not be a dramatic claim. It may be clarity about a complex subject, an organized method, a sense of companionship or a thoughtful path through a personal experience.
Test the promise against your chapter ideas. If a chapter does not help deliver it, revise the chapter’s purpose or consider whether it belongs elsewhere. A focused promise also supports book description writing, cover design decisions and book marketing, because readers can quickly understand why the book may matter to them.