62 And, indeed, in these three classes of examples, I see that no class of injury is passed over. For all matters in which we suffer any injustice are divided into two classes: of which the one is, where restitution cannot be made; the other, where it can. But in that case where restitution cannot be made, a compensation in revenge is usually sought. For what does it profit, that on being struck you strike in return? Is that part of the body which was injured for that reason restored to its original condition? But an excited mind desires such alleviations. Things of that sort, however, afford no pleasure to a healthy and firm one; nay, such an one judges rather that the other's infirmity is to be compassionately borne with, than that his own (which has no existence) should be soothed by the punishment of another.
63. Nor are we thus precluded from inflicting such punishment [requital] as avails for correction, and as compassion itself dictates; nor does it stand in the way of that course proposed, where one is prepared to endure more at the hand of him whom he wishes to set right. But no one is fit for inflicting this punishment except the man who, by the greatness of his love, has overcome that hatred wherewith those are wont to be inflamed who wish to avenge themselves. For it is not to be feared that parents would seem to hate a little son when, on committing an offense, he is beaten by them that he may not go on offending. And certainly the perfection of love is set before us by the imitation of God the Father Himself when it is said in what follows: “Love your enemies, do good to them that hate you, and pray for them which persecute you;” and yet it is said of Him by the prophet, “For whom the Lord loves He corrects; yea, He scourges every son whom He receives.” The Lord also says, “The servant that knows not his Lord's will, and does things worthy of stripes, shall be beaten with few stripes; but the servant that knows his Lord's will, and does things worthy of stripes, shall be beaten with many stripes.” No more, therefore, is sought for, except that he should punish to whom, in the natural order of things, the power is given; and that he should punish with the same goodwill which a father has towards his little son, whom by reason of his youth he cannot yet hate. For from this source the most suitable example is drawn, in order that it may be sufficiently manifest that sin can be punished in love rather than be left unpunished; so that one may wish him on whom he inflicts it not to be miserable by means of punishment, but to be happy by means of correction, yet be prepared, if need be, to endure with equanimity more injuries inflicted by him whom he wishes to be corrected, whether he may have the power of putting restraint upon him or not.
64. But great and holy men, although they at the time knew excellently well that that death which separates the soul from the body is not to be dreaded, yet, in accordance with the sentiment of those who might fear it, punished some sins with death, both because the living were struck with a salutary fear, and because it was not death itself that would injure those who were being punished with death, but sin, which might be increased if they continued to live. They did not judge rashly on whom God had bestowed such a power of judging. Hence it is that Elijah inflicted death on many, both with his own hand and by calling down fire from heaven; as was done also without rashness by many other great and godlike men, in the same spirit of concern for the good of humanity. And when the disciples had quoted an example from this Elias, mentioning to the Lord what had been done by him, in order that He might give to themselves also the power of calling down fire from heaven to consume those who would not show Him hospitality, the Lord reproved in them, not the example of the holy prophet, but their ignorance in respect to taking vengeance, their knowledge being as yet elementary; perceiving that they did not in love desire correction, but in hated desired revenge. Accordingly, after He had taught them what it was to love one's neighbour as oneself, and when the Holy Spirit had been poured out, whom, at the end of ten days after His ascension, He sent from above, as He had promised, there were not wanting such acts of vengeance, although much more rarely than in the Old Testament. For there, for the most part, as servants they were kept down by fear; but here mostly as free they were nourished by love. For at the words of the Apostle Peter also, Ananias and his wife, as we read in the Acts of the Apostles, fell down dead, and were not raised to life again, but buried.
65. But if the heretics who are opposed to the Old Testament will not credit this book, let them contemplate the Apostle Paul, whose writings they read along with us, saying with respect to a certain sinner whom he delivered over to Satan for the destruction of the flesh, “that the spirit may be saved.” And if they will not here understand death (for perhaps it is uncertain), let them acknowledge that punishment [requital] of some kind or other was inflicted by the apostle through the instrumentality of Satan; and that he did this not in hatred, but in love, is made plain by that addition, “that the spirit may be saved.” Or let them notice what we say in those books to which they themselves attribute great authority, where it is written that the Apostle Thomas imprecated on a certain man, by whom he had been struck with the palm of the hand, the punishment of death in a very cruel form, while yet commending his soul to God, that it might be spared in the world to come—whose hand, torn from the rest of his body after he had been killed by a lion, a dog brought to the table at which the apostle was feasting. It is allowable for us not to credit this writing, for it is not in the catholic canon; yet they both read it, and honour it as being thoroughly uncorrupted and thoroughly truthful, who rage very fiercely (with I know not what blindness) against the corporeal punishments which are in the Old Testament, being altogether ignorant in what spirit and at what stage in the orderly distribution of times they were inflicted.
Source: Our Lord's Sermon on the Mount (New Advent)