Some readers are surprised to learn that the books of the Bible are not placed in chronological order. The short answer for why is that those who compiled them did not believe a chronological reading was necessary to understanding. Instead, they used other criteria, namely genre, which is a type of work that loosely adheres to a particular style for a particular function.
The Jewish people look to Moses as the greatest prophet—the early Church would probably have agreed. It is fitting then that the Old Testament begins with the five books of Moses, also known as the books of the Law. These are followed by historical books, then poetry, then major and minor prophets to make 39 books in all.
The 27 New Testament books are ordered similarly in groupings by genre. The four gospels come first, followed by the historical book of Acts. Next, are Paul’s letters to the churches, grouped according to length, followed by personal letters, and ending with prophecy.