That the apostolic preaching is nothing other than the various predictions made by the prophets, proclaimed as having been realized in Jesus Christ, means that, on the one hand, the apostolic preaching is both the key to understanding the Old Testament and the confirmation of its fulfillment, while, on the other hand, it is the Old Testament which shapes the whole of the Christian revelation itself.

ST IRENAEUS OF LYONS, ON THE APOSTOLIC PREACHING, TRANSLATED WITH AN INTRODUCTION BY JOHN BEHR, 13.