3 To return to what I said of your not accepting everything in the Old Testament. You do not admit carnal circumcision, though that is what is written; nor resting from all occupation on the Sabbath, though that is enjoined; and instead of propitiating God, as Moses recommends, by offerings and sacrifices, you cast these things aside as utterly out of keeping with Christian worship, and as having nothing at all to recommend them. In some cases, however, you make a division, and while you accept one part, you reject the other.
Thus, in the Passover, which is also the annual feast of the Old Testament, while it is written that in this observance you must slay a lamb to be eaten in the evening, and that you must abstain from leaven for seven days, and be content with unleavened bread and bitter herbs, you accept the feast, but pay no attention to the rules for its observance. It is the same with the feast of Pentecost, or seven weeks, and the accompaniment of a certain kind and number of sacrifices which Moses enjoins: you observe the feast, but you condemn the propitiatory rites, which are part of it, because they are not in harmony with Christianity.
As regards the command to abstain from Gentile food, you are zealous believers in the uncleanness of things offered to idols, and of what has died of itself; but you are not so ready to believe the prohibition of swine's flesh, and hares, and conies, and mullets, and cuttle-fish, and all the fish that you have a relish for, although Moses pronounces them all unclean.
Source: Reply to Faustus the Manichaean (New Advent)