8 You say “it is of no importance what the quality of the fault may be in any case in which forgiveness is craved.” In this you would state the truth if the matter in question were the punishment and not the correction of men. Far be it from a Christian heart to be carried away by the lust of revenge to inflict punishment on any one. Far be it from a Christian, when forgiving any one his fault, to do otherwise than either anticipate or at least promptly answer the petition of him who asks forgiveness; but let his purpose in doing this be, that he may overcome the temptation to hate the man who has offended him, and to render evil for evil, and to be inflamed with rage prompting him, if not to do an injury, at least to desire to see the infliction of the penalties appointed by law; let it not be that he may relieve himself from considering the offender's interest, exercising foresight on his behalf, and restraining him from evil actions. For it is possible, on the one hand, that, moved by more vehement hostility, one may neglect the correction of a man whom he hates bitterly, and, on the other hand, that by correction involving the infliction of some pain one may secure the improvement of another whom he dearly loves.
9. I grant that, as you write, “penitence procures forgiveness, and blots out the offense,” but it is that penitence which is practised under the influence of the true religion, and which has regard to the future judgment of God; not that penitence which is for the time professed or pretended before men, not to secure the cleansing of the soul for ever from the fault, but only to deliver from present apprehension of pain the life which is so soon to perish. This is the reason why in the case of some Christians who confessed their fault, and asked forgiveness for having been involved in the guilt of that crime—either by their not protecting the church when in danger of being burned, or by their appropriating a portion of the property which the miscreants carried off—we believed that the pain of repentance had borne fruit, and considered it sufficient for their correction, because in their hearts is found that faith by which they could realize what they ought to fear from the judgment of God for their sin. But how can there be any healing virtue in the repentance of those who not only fail to acknowledge, but even persist in mocking and blaspheming Him who is the fountain of forgiveness? At the same time, towards these men we do not cherish any feeling of enmity in our hearts, which are naked and opened unto the eyes of Him whose judgment both in this life and in the life to come we dread, and in whose help we place our hope. But we think that we are even taking measures for the benefit of these men, if, seeing that they do not fear God, we inspire fear in them by doing something whereby their folly is chastened, while their real interests suffer no wrong. We thus prevent that God whom they despise from being more grievously provoked by their greater crimes, to which they would be emboldened by a disastrous assurance of impunity, and we prevent their assurance of impunity from being set forth with even more mischievous effect as an encouragement to others to imitate their example. In fine, on behalf of those for whom you make intercession to us, we intercede before God, beseeching Him to turn them to Himself, and to teach them the exercise of genuine and salutary repentance, purifying their hearts by faith.
10. Behold, then, how we love those men against whom you suppose us to be full of anger—loving them, you must permit me to say, with a love more prudent and profitable than you yourself cherish towards them; for we plead on their behalf that they may escape much greater afflictions, and obtain much greater blessings. If you also loved these men, not in the mere earthly affections of men, but with that love which is the heavenly gift of God, and if you were sincere in writing to me that you gave ear with pleasure to me when I was recommending to you the worship and religion of the Supreme God, you would not only wish for your countrymen the blessings which we seek on their behalf, but you would yourself by your example lead them to their possession. Thus would the whole business of your interceding with us be concluded with abundant and most reasonable joy. Thus would your title to that heavenly fatherland, in regard to which you say that you welcomed my counsel that you should fix your eye upon it, be earned by a true and pious exercise of your love for the country which gave you birth, when seeking to make sure to your fellow citizens, not the vain dream of temporal happiness, nor a most perilous exemption from the due punishment of their faults, but the gracious gift of eternal blessedness.
11. You have here a frank avowal of the thoughts and desires of my heart in this matter. As to what lies concealed in the counsels of God, I confess it is unknown to me; I am but a man; but whatever it be, His counsel stands most sure, and incomparably excels in equity and in wisdom all that can be conceived by the minds of men. With truth is it said in our books, “There are many devices in a man's heart; but the counsel of the Lord, that shall stand.” Wherefore, as to what time may bring forth, as to what may arise to simplify or complicate our procedure, in short, as to what desire may suddenly be awakened by the fear of losing or the hope of retaining present possessions; whether God shall show Himself so displeased by what they have done that they shall be punished with the more weighty and severe sentence of a disastrous impunity, or shall appoint that they shall be compassionately corrected in the manner which we propose, or shall avert whatever terrible doom was being prepared for them, and convert it into joy by some more stern but more salutary correction, leading to their turning unfeignedly to seek mercy not from men but from Himself—all this He knows; we know not. Why, then, should your Excellency and I be spending toil in vain over this matter before the time? Let us for a little while lay aside a care the hour of which has not yet come, and, if you please, let us occupy ourselves with that which is always pressing. For there is no time at which it is not both suitable and necessary for us to consider in what way we can please God; because for a man to attain completely in this life to such perfection that no sin whatever shall remain in him is either impossible or (if perchance any attain to it) extremely difficult: wherefore without delay we ought to flee at once to the grace of Him to whom we may address with perfect truth the words which were addressed to some illustrious man by a poet, who declared that he had borrowed the lines from a Cumæan oracle, or ode of prophetic inspiration: “With you as our leader, the obliteration of all remaining traces of our sin shall deliver the earth from perpetual alarm.” For with Him as our leader, all sins are blotted out and forgiven; and by His way we are brought to that heavenly fatherland, the thought of which as a dwelling-place pleased you greatly when I was to the utmost of my power commending it to your affection and desire.
Source: Letters (New Advent)