14 But why may I not say regarding these institutions of the old economy, that they are neither good nor bad: not good, since men are not by them justified, they having been only shadows predicting the grace by which we are justified; and not bad, since they were divinely appointed as suitable both to the time and to the people? Why may I not say this, when I am supported by that saying of the prophet, that God gave unto His people “statutes that were not good”? For we have in this perhaps the reason of his not calling them “bad,” but calling them “not good,” i.e. not such that either by them men could be made good, or that without them men could not possibly become good. I would esteem it a favour to be informed by your Sincerity, whether any saint, coming from the East to Rome, would be guilty of dissimulation if he fasted on the seventh day of each week, excepting the Saturday before Easter. For if we say that it is wrong to fast on the seventh day, we shall condemn not only the Church of Rome, but also many other churches, both neighbouring and more remote, in which the same custom continues to be observed. If, on the other hand, we pronounce it wrong not to fast on the seventh day, how great is our presumption in censuring so many churches in the East, and by far the greater part of the Christian world! Or do you prefer to say of this practice, that it is a thing indifferent in itself, but commendable in him who conforms with it, not as a dissembler, but from a seemly desire for the fellowship and deference for the feelings of others? No precept, however, concerning this practice is given to Christians in the canonical books. How much more, then, may I shrink from pronouncing that to be bad which I cannot deny to be of divine institution!— this fact being admitted by me in the exercise of the same faith by which I know that not through these observances, but by the grace of God through our Lord Jesus Christ, I am justified.
15. I maintain, therefore, that circumcision, and other things of this kind, were, by means of what is called the Old Testament, given to the Jews with divine authority, as signs of future things which were to be fulfilled in Christ; and that now, when these things have been fulfilled, the laws concerning these rights remained only to be read by Christians in order to their understanding the prophecies which had been given before, but not to be of necessity practised by them, as if the coming of that revelation of faith which they prefigured was still future. Although, however, these rites were not to be imposed upon the Gentiles, the compliance with them, to which the Jews had been accustomed, was not to be prohibited in such a way as to give the impression that it was worthy of abhorrence and condemnation. Therefore slowly, and by degrees, all this observance of these types was to vanish away through the power of the sound preaching of the truth of the grace of Christ, to which alone believers would be taught to ascribe their justification and salvation, and not to those types and shadows of things which till then had been future, but which were now newly come and present, as at the time of the calling of those Jews whom the personal coming of our Lord and the apostolic times had found accustomed to the observance of these ceremonial institutions. The toleration, for the time, of their continuing to observe these was enough to declare their excellence as things which, though they were to be given up, were not, like the worship of idols, worthy of abhorrence; but they were not to be imposed upon others, lest they should be thought necessary, either as means or as conditions of salvation. This was the opinion of those heretics who, while anxious to be both Jews and Christians, could not be either the one or the other. Against this opinion you have most benevolently condescended to warn me, although I never entertained it. This also was the opinion with which, through fear, Peter fell into the fault of pretending to yield concurrence, though in reality he did not agree with it; for which reason Paul wrote most truly of him, that he saw him not walking uprightly, according to the truth of the gospel, and most truly said of him that he was compelling the Gentiles to live as did the Jews. Paul did not impose this burden on the Gentiles through his sincerely complying, when it was needful, with these ceremonies, with the design of proving that they were not to be utterly condemned (as idol-worship ought to be); for he nevertheless constantly preached that not by these things, but by the grace revealed to faith, believers obtain salvation, lest he should lead any one to take up these Jewish observances as necessary to salvation. Thus, therefore, I believe that the Apostle Paul did all these things honestly, and without dissimulation; and yet if any one now leave Judaism and become a Christian, I neither compel nor permit him to imitate Paul's example, and go on with the sincere observance of Jewish rites, any more than you, who think that Paul dissembled when he practised these rites, would compel or permit such an one to follow the apostle in that dissimulation.
16. Shall I also sum up “the matter in debate, or rather your opinion concerning it” (to quote your own expression)? It seems to me to be this: that after the gospel of Christ has been published, the Jews who believe do rightly if they offer sacrifices as Paul did, if they circumcise their children as Paul circumcised Timothy, and if they observe the “seventh day of the week, as the Jews have always done, provided only that they do all this as dissemblers and deceivers.” If this is your doctrine, we are now precipitated, not into the heresy of Ebion, or of those who are commonly called Nazarenes, or any other known heresy, but into some new error, which is all the more pernicious because it originates not in mistake, but in deliberate and designed endeavour to deceive. If, in order to clear yourself from the charge of entertaining such sentiments, you answer that the apostles were to be commended for dissimulation in these instances, their purpose being to avoid giving offense to the many weak Jewish believers who did not yet understand that these things were to be rejected, but that now, when the doctrine of Christ's grace has been firmly established throughout so many nations, and when, by the reading of the Law and the Prophets throughout all the churches of Christ, it is well known that these are not read for our observance, but for our instruction, any man who should propose to feign compliance with these rites would be regarded as a madman. What objection can there be to my affirming that the Apostle Paul, and other sound and faithful Christians, were bound sincerely to declare the worth of these old observances by occasionally honouring them, lest it should be thought that these institutions, originally full of prophetic significance, and cherished sacredly by their most pious forefathers, were to be abhorred by their posterity as profane inventions of the devil? For now, when the faith had come, which, previously foreshadowed by these ceremonies, was revealed after the death and resurrection of the Lord, they became, so far as their office was concerned, defunct. But just as it is seemly that the bodies of the deceased be carried honourably to the grave by their kindred, so was it fitting that these rites should be removed in a manner worthy of their origin and history, and this not with pretence of respect, but as a religious duty, instead of being forsaken at once, or cast forth to be torn in pieces by the reproaches of their enemies, as by the teeth of dogs. To carry the illustration further, if now any Christian (though he may have been converted from Judaism) were proposing to imitate the apostles in the observance of these ceremonies, like one who disturbs the ashes of those who rest, he would be not piously performing his part in the obsequies, but impiously violating the sepulchre.
Source: Letters (New Advent)