It need to display readers why they need to read through your book and allow them to know what they might anticipate; it’s an advert for the book. It's not necessarily your personal assertion on why you wrote the book. (This usually goes on the interior book jacket flap for https://pinpdf.com/maple-publishers-redefining-the-self-publishing-experience-c1f5ccc50e46ebccbf6efb3ea690cb05.html