The Threefold Division of the Old Testament, Law, Prophets, and Writings

The threefold division of the Old Testament, law, prophets, writings, where do we get the names for each of those sections? Well this is something Jim will cover in more detail, I'm sure. But as you look at the books that are in each section, what you'll notice is that each section has history books. And curiously in the writings, you have these history books like Esther, Ezra, Nehemiah, Chronicles.