There is so much thinking that needs to go into a book before it’s ready to be submitted: finding, then refining, the concept.
We’ve all learned to think about crafting books in terms of writing.
For a book proposal or a novel’s query letter to have any chance of success, a writer needs to be able to present the concept of the book.
So you can explain why anyone would want to read it.
To prove how it is different from other books.
To know exactly who needs to read it.
And to understand why you need to write it.