6 But how can you venture to quote this verse against me? Or why should it be against me only, when it is as much against yourself? If Christ does not destroy the law and the prophets, neither must Christians do so. Why then do you destroy them? Do you begin to perceive that you are no Christian? How can you profane with all kinds of work the day pronounced sacred in the law and in all the prophets, on which they say that God, the maker of the world, himself rested, without dreading the penalty of death pronounced against Sabbath-breakers, or the curse on the transgressor?
How can you refuse to receive in your person the unseemly mark of circumcision, which the law and all the prophets declare to be honorable, especially in the case of Abraham, after what was thought to be his faith; for does not the God of the Jews proclaim that whosoever is without this mark of infamy shall perish from his people? How can you neglect the appointed sacrifices, which were made so much of both by Moses and the prophets under the law, and by Abraham in his faith? And how can you defile your souls by making no distinction in foods, if you believe that Christ came not to destroy these things, but to fulfill them?
Why do you discard the annual feast of unleavened bread, and the appointed sacrifice of the lamb, which, according to the law and the prophets, is to be observed for ever? Why, in a word, do you treat so lightly the new moons, the baptisms, and the feast of tabernacles, and all the other carnal ordinances of the law and the prophets, if Christ did not destroy them? I have therefore good reason for saying that, in order to justify your neglect of these things, you must either abandon your profession of being Christ's disciple, or acknowledge that Christ himself has already destroyed them; and from this acknowledgment it must follow, either that this text is spurious in which Christ is made to say that he came not to destroy the law, but to fulfill it, or that the words have an entirely different meaning from what you suppose.
Source: Reply to Faustus the Manichaean (New Advent)