St. Paul in Galatians 5:1-6 stated that the observance of circumcision and the requirements of the Law of Moses from the Old Testament were abrogated and no longer binding. The only remaining elements of the Old Testament that are required are the moral law – the ceremonial laws are not. And that is why the requirement for wearing tassels on your clothes (cf. Deuteronomy 22:12), abstaining from pork or shellfish, or not using two different species to plow a field at the same time are abrogated. The Jews count 613 different laws, but all ceremonial laws do not apply any longer since the New Testament has completed and fulfilled the Old Testament.
The laws of Leviticus have been abolished. Only the moral laws of the Old Testament (e.g. the Ten Commandments) remain. The Apostles and the Early Church definitively taught that the Law of Moses on dietary restrictions no longer applied.
Why Do Catholics Then Have Certain Restrictions on Days like Fridays?
To ignore the law of fasting or abstinence from meat is a grave sin. Why? Because it is an act of disobedience to God's Church. We do not abstain from meat on Fridays for instance because the meat is unclean or evil. It is the act of disobedience that is evil. As Fr. Michael Müller remarks in his Familiar Explanation of Christian Doctrine from 1874: "It is not the food, but the disobedience that defiles a man."
To eat meat on a forbidden day unintentionally, for instance, is no sin. As the Scriptures affirm it is not what goes into one's mouth that defiles a man but that disobedience which comes from the soul (cf. Matthew 15:11). But to eat meat on a Friday or to refuse the law of fasting on required days is a serious sin because of disobedience.
A Review of The Baltimore Catechism:
Q. 1136. How many kinds of laws had the Jews before the coming of Our Lord?
A. Before the coming of Our Lord the Jews had three kinds of laws:
1. Civil laws, regulating the affairs of their nation;
2. Ceremonial laws, governing their worship in the temple;
3. Moral laws, guiding their religious belief and actions.
Q. 1137. To which of these laws did the Ten Commandments belong?
A. The Ten Commandments belong to the moral law, because they are a compendium or short account of what we must do in order to save our souls; just as the Apostles' Creed is a compendium of what we must believe.
Q. 1138. When did the civil and ceremonial laws of the Jews cease to exist?
A. The civil laws of the Jews ceased to exist when the Jewish people, shortly before the coming of Christ, ceased to be an independent nation. The ceremonial laws ceased to exist when the Jewish religion ceased to be the true religion; that is, when Christ established the Christian religion, of which the Jewish religion was only a figure or promise.
Q. 1139. Why were not also the moral laws of the Jews abolished when the Christian religion was established?
A. The moral laws of the Jews could not be abolished by the establishment of the Christian religion because they regard truth and virtue and have been revealed by God, and whatever God has revealed as true must be always true, and whatever He has condemned as bad in itself must be always bad.