“…what the Old Testament promised, the New Testament made visible; what the former announces in a hidden way, the latter openly proclaims as present. Therefore the Old Testament is a prophecy of the New Testament; and the best commentary on the Old Testament is the New Testament.” (Pope St. Gregory the Great, Doctor of the Church, Homiliae in Ezechielem I, VI, 15: PL 76, 836B.)
The Memorial of Pope St. Gregory the Great, Doctor of the Church (A.D. 540 – 604) is September 3.