Novatian: On the Jewish Meats IV-VII
In addition to each forbidden animal providing a sermon on sin (see the previous chapters), Novatian argues in the conclusion to the treatise that the OT dietary laws were provided to teach us self-restraint and the dangers of luxury.
Luxury is inimical to holiness. For how shall religion be spared by it, when modesty is not spared? Luxury does not entertain the fear of God; since while pleasures hurry it on, it is carried forward to the sole daring of its desires...And although the specific tenets of those laws have now been overturned by the coming of Christ, the basic principles underlying them remains in effect. Now we understand that these laws are not fulfilled by a proper diet, but are fulfilled 1) in Christ and 2) in the holy life of a Christian, for "the meat, I say, true, and holy, and pure, is a true faith, an unspotted conscience, and an innocent soul." And again "God rejoices in our faith alone, in our innocency alone, in our truth alone, in our virtues alone. And these dwell not in our belly, but in our soul..."
The Gospel, at the end of the day, should call us to be temperate in a way that is consistent not with the external observations of the OT law, but with the life it called OT believers to live. That is, a life of moderation, generosity, and holiness dedicated to war against sin and love of God and neighbor.
This treatise is excellent, so read it!