17 I acknowledge that in the statement contained in my letter, to the effect that the reason why Paul undertook (although he was an apostle of Christ) to perform certain rites, was that he might show that these ceremonies were not pernicious to those who desired to continue that which they had received by the Law from their fathers, I have not explicitly enough qualified the statement, by adding that this was the case only in that time in which the grace of faith was at first revealed; for at that time this was not pernicious. These observances were to be given up by all Christians step by step, as time advanced; not all at once, lest, if this were done, men should not perceive the difference between what God by Moses appointed to His ancient people, and the rites which the unclean spirit taught men to practise in the temples of heathen deities. I grant, therefore, that in this your censure is justifiable, and my omission deserved rebuke. Nevertheless, long before the time of my receiving your letter, when I wrote a treatise against Faustus the Manichæan, I did not omit to insert the qualifying clause which I have just stated, in a short exposition which I gave of the same passage, as you may see for yourself if you kindly condescend to read that treatise; or you may be satisfied in any other way that you please by the bearer of this letter, that I had long ago published this restriction of the general affirmation. And I now, as speaking in the sight of God, beseech you by the law of charity to believe me when I say with my whole heart, that it never was my opinion that in our time, Jews who become Christians were either required or at liberty to observe in any manner, or from any motive whatever, the ceremonies of the ancient dispensation; although I have always held, in regard to the Apostle Paul, the opinion which you call in question, from the time that I became acquainted with his writings. Nor can these two things appear incompatible to you; for you do not think it is the duty of any one in our day to feign compliance with these Jewish observances, although you believe that the apostles did this.
18. Accordingly, as you in opposing me affirm, and, to quote your own words, “though the world were to protest against it, boldly declare that the Jewish ceremonies are to Christians both hurtful and fatal, and that whoever observes them, whether he was originally Jew or Gentile, is on his way to the pit of perdition,” I entirely endorse that statement, and add to it, “Whoever observes these ceremonies, whether he was originally Jew or Gentile, is on his way to the pit of perdition, not only if he is sincerely observing them, but also if he is observing them with dissimulation.” What more do you ask? But as you draw a distinction between the dissimulation which you hold to have been practised by the apostles, and the rule of conduct befitting the present time, I do the same between the course which Paul, as I think, sincerely followed in all these examples then, and the matter of observing in our day these Jewish ceremonies, although it were done, as by him, without any dissimulation, since it was then to be approved, but is now to be abhorred. Thus, although we read that “the law and the prophets were until John,” and that “therefore the Jews sought the more to kill Him, because He not only had broken the Sabbath, but said also that God was His Father, making Himself equal with God,” and that “we have received grace for grace for the law was given by Moses, but grace and truth came by Jesus Christ;” and although it was promised by Jeremiah that God would make a new covenant with the house of Judah, not according to the covenant which He made with their fathers; nevertheless I do not think that the Circumcision of our Lord by His parents was an act of dissimulation. If any one object that He did not forbid this because He was but an infant, I go on to say that I do not think that it was with intention to deceive that He said to the leper, “Offer for your cleansing those things which Moses commanded for a testimony unto them,” — thereby adding His own precept to the authority of the law of Moses regarding that ceremonial usage. Nor was there dissimulation in His going up to the feast, as there was also no desire to be seen of men; for He went up, not openly, but secretly.
19. But the words of the apostle himself may be quoted against me: “Behold, I Paul say unto you, that if you be circumcised, Christ shall profit you nothing.” It follows from this that he deceived Timothy, and made Christ profit him nothing, for he circumcised Timothy. Do you answer that this circumcision did Timothy no harm, because it was done with an intention to deceive? I reply that the apostle has not made any such exception. He does not say, If you be circumcised without dissimulation, any more than, If you be circumcised with dissimulation. He says unreservedly, “If you be circumcised, Christ shall profit you nothing.” As, therefore, you insist upon finding room for your interpretation, by proposing to supply the words, “unless it be done as an act of dissimulation,” I make no unreasonable demand in asking you to permit me to understand the words, “if you be circumcised,” to be in that passage addressed to those who demanded circumcision, for this reason, that they thought it impossible for them to be otherwise saved by Christ. Whoever was then circumcised because of such persuasion and desire, and with this design, Christ assuredly profited him nothing, as the apostle elsewhere expressly affirms, If righteousness come by the law, Christ is dead in vain. The same is affirmed in words which you have quoted: “Christ has become of no effect to you, whosoever of you is justified by the law; you are fallen from grace.” His rebuke, therefore, was addressed to those who believed that they were to be justified by the law,— not to those who, knowing well the design with which the legal ceremonies were instituted as foreshadowing truth, and the time for which they were destined to be in force, observed them in order to honour Him who appointed them at first. Wherefore also he says elsewhere, “If you be led of the Spirit, you are not under the law,” — a passage from which you infer, that evidently “he has not the Holy Spirit who submits to the Law, not, as our fathers affirmed the apostles to have done, feignedly under the promptings of a wise discretion, but”— as I suppose to have been the case— “sincerely.”
Source: Letters (New Advent)