The Ceremonial Law as Acquired Virtue
The commandments of the Law of Moses require both interior and exterior acts. There are commandments which pertain to the heart (love of G-d, to love of neighbor, fear of G-d etc.) and commandments which pertain to the body (resting on the Sabbath, eating kosher food, etc.). Virtually all the commandments of Jesus relate to interior acts. True, he requires acts of charity. He requires us to feed the hungry, clothe the naked, visit the sick etc. but that is because those acts bear witness to love. It is the love that he requires, and it has been said by Catholic saints that, without love, even such acts are meaningless.
No Jewish theologian would ever say that about the commandments of the Law of Moses. The commandments of the ceremonial law have a profound religious value even if they are observed with no more than the minimal intention of acting to fulfill them. The acts of the ceremonial Law are spiritual exercises that operate on the heart through the body, so that they are efficacious and beneficial even when they are done as though all that was required was the external act itself (though, of course, doing them in that way reaps only the minimum benefit). That is why Paul could refer to himself as "blameless under the Law” (Phi. 3:6) even though he was acting out of "a righteousness of my own, based on law." That "righteousness of my own, based on law" is sufficient to move the body in the service of G-d. A Jew who does not recognize the possibility of moving the heart to G-d, as St. Paul clearly didn’t before his conversion (see Romans 7), is likely to believe that the external acts of the commandments are necessary for salvation, not because G-d is keeping a record of what was and was not done, but because it is only through the external acts that the heart—the essential man—is configured to holiness. He knows no other way.
Jesus taught that through faith, in cooperation with grace, a person can act upon his heart directly. That is why the commandments of Jesus all pertain to the heart. They are interior acts of devotion which are only possible in a state of grace. Some inferred from Jesus’ teaching that it was no longer necessary to act upon the heart through the body, i.e., through the acts of the ceremonial Law. So Jesus reaffirmed the importance of keeping the commandments (Matt. 5 & 23). Why, indeed, were they still important? Because, among other things, the commandments are to faith as the acquired moral virtues are to the infused virtues. A person who has, through education and instruction, acquired virtues conducts himself in a way which is consistent with man’s stature as a rational being. The infused virtues then perfect his conduct, as faith perfects reason and grace perfects nature. When a man lacks the acquired virtues, he can still receive the infused virtues, but he finds it hard to act upon them. He is more likely to experience infused virtue as a bad conscience rather than as an inspiration, and he may even reject it, because in the absence of virtue, he may have chosen for himself a way of life which cannot be reconciled with faith.
The ceremonial law is a way of life, passed on from generation to generation, through education and repetition. Ordained by G-d, it is nevertheless, a natural pattern of conduct—natural because it can be maintained out of "a righteousness of my own," even by a person who is not in a state of grace—that is directed to man’s supernatural end. The observance of the commandments prepares the Jew for the perfection which grace brings, just as the acquired virtues prepare a person for the perfection of the infused virtues.The Ceremonial Law directs a person to live in a way that is consistent, not only with his stature as a rational being, but as a man of faith and child of G-d.
Now that the Church no longer suppresses the observance of the Law as though it implied a denial of the adequacy of Christian faith for salvation or, as a figure of Christ that anticipated him, a denial that he has come, the question arises: if the commandments are comparable to the acquired virtues with respect to faith, why shouldn't Christians keep them? There are many reasons, but I think that the ultimate reason is that the obligation to keep them arose out of the covenant of Sinai, and, of course, that covenant was made only with the people who were redeemed from Egypt, with the Children of Israel.
The rabbis teach us that derech eretz, i.e., the acquired virtues, precede Torah. The Ceremonial Law is not a substitute for the acquired virtues, but adds something to them which has specific importance for Jewish faith.Jesus admonished his Jewish disciples to keep the Law because, for the Jew, Christian faith perfects the faith which the Ceremonial Law promotes. Jesus wasn’t teaching the Jewish people another religion. He was teaching them Judaism. The Gentile does not know Christian faith as a perfection of Judaism. He’s not Jewish. He knows Christian faith as the universal faith, as the way that G-d addresses all mankind and calls him to holiness. That is the catholic faith of the Church and, within the Catholic faith, the sacramentals serve the purpose that the ceremonial Law has in Jewish faith.