Christ subdivides the books of the Old Testament into Moses, the Prophets, and the Psalms (Luke 24:44). Moses is the root and stem; the prophets’ books constitute the tree with its fruits; the Psalms are the flowers. We are not convinced of what some people say, that the title “Psalms” is taken generally for the books limited in number, which are Job, Psalms, Proverbs, Ecclesiastes, Song of Songs, and Lamentations. we feel that it more likely means the Book of Psalms specifically. In this way, then, Moses as the source and spring, or root and trunk, and the Psalms as the flowers of Scripture are distinguished from the rest of the prophetic books. In Luke 16:29 and Acts 26:22, Christ and Paul divide the books of the Old Testament into Moses and the Prophets, that is, into Mosaic and prophetic books, because Moses is the originator and leader of the other prophets.
On the Nature of Theology and on Scripture