4 If one of the Nazareans, or Symmachians, as they are sometimes called, were arguing with me from these words of Jesus that he came not to destroy the law, I should find some difficulty in answering him. For it is undeniable that, at his coming, Jesus was both in body and mind subject to the influence of the law and the prophets. Those people, moreover, whom I allude to, practise circumcision, and keep the Sabbath, and abstain from swine's flesh and such like things, according to the law, although they profess to be Christians.
They are evidently misled as well as you, by this verse in which Christ says that he came not to destroy the law, but to fulfill it. It would not be easy to reply to such opponents without first getting rid of this troublesome verse. But with you I have no difficulty, for you have nothing to go upon; and instead of using arguments, you seem disposed, in mere mischief, to induce me to believe that Christ said what you evidently do not yourself believe him to have said. On the strength of this verse you accuse me of dullness and evasiveness, without yourself giving any indication of keeping the law instead of destroying it.
Do you too, like a Jew or a Nazarean, glory in the obscene distinction of being circumcised? Do you pride yourself in the observance of the Sabbath? Can you congratulate yourself on being innocent of swine's flesh? Or can you boast of having gratified the appetite of the Deity by the blood of sacrifices and the incense of Jewish offerings? If not, why do you contend that Christ came not to destroy the law, but to fulfill it?
Source: Reply to Faustus the Manichaean (New Advent)