8 Christ also fulfilled the prophecies, because the promises of God were made good in Him. As the apostle says in the verse quoted above, "The promises of God are in Him yea." Again, he says: "Now I say that Jesus Christ was a minister of the circumcision for the truth of God, to confirm the promises made unto the fathers." Whatever, then, was promised in the prophets, whether expressly or in figure, whether by words or by actions, was fulfilled in Him who came not to destroy the law and the prophets, but to fulfill them.
You do not perceive that if Christians were to continue in the use of acts and observances by which things to come were prefigured, the only meaning would be that the things prefigured had not yet come. Either the thing prefigured has not come, or if it has, the figure becomes superfluous or misleading. Therefore, if Christians do not practise some things enjoined in the Hebrews by the prophets, this, so far from showing, as you think, that Christ did not fulfill the prophets, rather shows that He did.
So completely did Christ fulfill what these types prefigured, that it is no longer prefigured. So the Lord Himself says: "The law and the prophets were until John." For the law which shut up transgressors in increased guilt, and to the faith which was afterwards revealed, became grace through Jesus Christ, by whom grace superabounded. Thus the law, which was not fulfilled in the requirement of the letter, was fulfilled in the liberty of grace. In the same way, everything in the law that was prophetic of the Saviour's advent, whether in words or in typical actions, became truth in Jesus Christ.
For "the law was given by Moses, but grace and truth came by Jesus Christ." At Christ's advent the kingdom of God began to be preached; for the law and the prophets were until John: the law, that its transgressors might desire salvation; the prophets, that they might foretell the Saviour. No doubt there have been prophets in the Church since the ascension of Christ. Of these prophets Paul says: "God has set some in the Church, first apostles, secondarily prophets, thirdly teachers," and so on. It is not of these prophets that it was said, "The law and the prophets were until John," but of those who prophesied the first coming of Christ, which evidently cannot be prophesied now that it has taken place.
Source: Reply to Faustus the Manichaean (New Advent)