[Ambrose wrote this letter in the 4th century.]
68. To Clementianus
Today, my son, you heard the lesson in the Apostle that ‘The Law has been our tutor unto Christ, that we might be justified by faith.’ It seems to me that by this one text those questions are resolved which ordinarily trouble many persons. There are those who say: ‘Since God gave the Law to Moses, why is it that there are many things in the Law which seem made void now by the Gospel? And how can the Author of the two Testaments be one and the same, when a thing permitted in the Law was no longer permitted when the Gospel came, such as bodily circumcision, though it was then given only as a sign, in order that the reality of spiritual circumcision might be retained? But why was it given even for a sign? Why is there such a difference of opinion, so that circumcision, being then considered piety, is now thought an impiety? Further, according to the Law it was ordained that the Sabbath be kept as a holiday, and if one carried a bundle of sticks he was guilty of death, but now we see that very day devoted to carrying burdens and conducting business without any penalty being attached. There are many commandments of the Law which seem to have ceased at the present time.’
Let us consider the reason for this, for not unintentionally did the Apostle say that ‘The Law has been our tutor unto Christ.’ Who has a tutor, an older person or a youth? Undoubtedly, a youth or child, that is, one of tender age, for pedagogus, as the word is rendered in Latin, means a child’s teacher; he cannot impart perfect precepts to an imperfect age, because it cannot bear them. Then, through the Prophet, the God of the Law says: ‘I shall give you statutes that are not good,’ that is, not perfect, for perfect is surely what is good. But the same God has preserved the most perfect things for the Gospel, as He says: ‘I have not come to destroy the Law, but to fulfill it.’
What, then, was the cause of this diversity if not man’s changeableness? He knew that the Jewish people were stiff-necked, prone to fall, base, inclined to unbelief, who heard with their ears and did not heed, who saw with their eyes and did not see, being fickle with the instability of infancy, heedless of commands. And so He provided the Law as a tutor for the unstable disposition and weak mind of His people, and moderating the very precepts of the Law, He desired one to be read, the other to be understood. Thus, the fool would at least keep watch over what he was reading and not depart from the instruction of the letter, while the wise would understand the thought of God’s mind which the letter did not convey; the man lacking judgment would keep the command of the Law, the man of judgment its mystery. Thus does the Law hold a sword’s severity, as the tutor does his rod, in order to awe by threatening punishment of the weakness of an imperfect people. Yet, the Gospel has a gentleness by which sins are forgiven.
Rightly, then, does Paul say that ‘the letter kills, but the spirit gives life.’ The letter circumcised a small part of the body, the understanding spirit keeps the circumcision of the entire soul and body, so that chastity might be preserved, frugality loved, with the unnecessary parts cut off (for nothing is so unnecessary as the vices of greed, the sins of lust, which did not belong to nature but which sin has caused). Bodily circumcision is the symbol, but the reality is the spiritual circumcision; the one cuts off a member, the other sin. Nature has created nothing imperfect in man, nor has she bade it be removed as unnecessary. However, in order that those who cut off part of their body might realize that there is more need for their sins to be cut off, and those persons cut down who led them to sin, even though they are joined by a certain bodily union, you have the words: ‘If thy right hand is an occasion of sin to thee, cut it off and cast it from thee; for it is better for thee that one of thy members should be lost than that thy whole body should go into hell.’ To the Jews, therefore, like children, precepts are not given in full but only in part, and they who could not keep the whole body clean are bidden to keep clean, as it were, only one part of it.1
 Ambrose of Milan, Saint Ambrose: Letters, ed. Roy Joseph Deferrari, trans. Mary Melchior Beyenka, vol. 26, The Fathers of the Church (Washington, DC: The Catholic University of America Press, 1954), 405–407.