Because it is not a fraud. No doubt you take as "Gospel" the other old books like Josephus, and the ancient Greek and Latin books. Yet of all the ancient books, the book about which we can have the greatest confidence is the Bible. Just to show how reliable it is as a book (you may reject what it says) the book of Isiah (Old Testament for the ignorant) was found in amongst the Dead Sea Scrolls. The book was placed there about 2000 yrs ago. That old copy was almost exactly (Maybe one of two words different here and there) the same as received and in current Bibles.
