From J. I. Packer’s foreword to the 25th anniversary edition of Edmund Clowney’s masterpiece, The Unfolding Mystery: Discovering Christ in the Old Testament (P&R Publishing, 2013):
The Bible is a unity. That is, perhaps, the most amazing of all the amazing things that are true of it. It consists of sixty-six separate units, written over more than a thousand years against a wide variety of cultural backgrounds, by people who for the most part worked independently of each other and show no awareness that their books would become canonical Scripture. The books themselves are of all kinds: prose jostling poetry, hymns rubbing shoulders with history, sermons with statistics, letters with liturgies, lurid visions with a love song.
Why do we bind up this collection between the same two covers, call it The Holy Bible, and treat it as one book? One justification for doing this–one of many–is that the collection as a whole, once we start to explore it, proves to have an organic coherence that is simply stunning. Books written centuries apart seem to have been designed for the express purpose of supplementing and illuminating each other. There is throughout one leading character (God the Creator), one historical perspective (world redemption), one local figure (Jesus of Nazareth, who is both Son of God and Savior), and one solid body of harmonious teaching about God and godliness. Truly the inner unity of the Bible is miraculous: a sign and a wonder, challenging the unbelief of our skeptical age.
The Bible is full of diversity, yes. But all of its diversity is clothed in unity. Many kinds of teaching in many different ways (cf. Hebrews 1:1-2), yet one coherent message without contradictions throughout all the centuries, locations, and books. Wow! Only a God who is sovereign over history could orchestrate that. And He did! Let’s read His book!