Matthew 18:15

Let us look well whether this precept extends to all sin; for what if any one sin any of those sins which are unto death, such as unnatural crimes, adultery, homicide, or effeminacy, it cannot be meant that such as these are to be admonished privately, and if he hear you, forthwith to say that you have gained him. And not rather first put him out of the Church, or only when remaining obstinate after monition before witnesses, and by the Church? One man, looking at the infinite mercy of Christ, will say, that since the words of Christ make no distinction of sins, it is to go against Christ's mercy to limit His words only to little sins. Another, on the other hand, considering the words carefully, will aver, that they are not spoken of every sin; for that he that is guilty of those great sins is not a brother, but is called a brother, with whom, according to the Apostle, we ought not so much as to eat. But as they who expound this as referring to every sin give encouragement to the careless to sin; so, on the other hand, he, who teaches that one having sinned in little sins and such as are not deadly, is, when he has spurned the admonition of the witnesses and the Church, to be held as a heathen and a publican, seems to introduce too great severity. For whether he finally perishes, we are not able to decide. First, because he who has been thrice told of his fault and not hearkened, may hearken the fourth time; secondly, because sometimes a man does not receive according to his deeds, but beyond his trespass, which is good for him in this world; lastly, because He said not alone, Let him be as a heathen, but Let him be to thee. Whosoever then when reproved three times in a light trespass, does not amend, him we ought to hold for a heathen and a publican, avoiding him, that he may be brought to confusion. But whether he is esteemed of God also as a heathen and a publican, is not ours to decide, but is in the judgment of God.

For, since He had used vehement language against them that cause offense, and on every hand had moved them to fear; in order that the offended might not in this way on the other hand become supine, neither supposing all to be cast upon others, should be led on to another vice, soften in themselves, and desiring to be humored in everything, and run upon the shoal of pride; seest thou how He again checks them also, and commands the telling of the faults to be between the two alone, lest by the testimony of the many he should render his accusation heavier, and the other, become excited to opposition, should continue incorrigible. Wherefore He saith, "Between thee and him alone," and, "If he shall hear thee, thou hast gained thy brother." What is, "If he shall hear thee?" If he shall condemn himself, if he shall be persuaded that he has done wrong. "Thou hast gained thy brother." He did not say, Thou hast a sufficient revenge, but, "Thou hast gained thy brother," to show that there is a common loss from the enmity. For He said not, "He hath gained himself only," but, "thou too hast gained him," whereby He showed that both the one and the other were losers before this, the one of his brother, the other of his own salvation. This, when He sat on the mount also, He advised; at one time bringing him who has given the pain to him that had been pained, and saying, "Be reconciled to thy brother," and at another commanding him that had been wronged to forgive his neighbor. For He taught men to say, "Forgive us our debts, like as we forgive our debtors." But here He is devising another mode. For not him that gave the pain, doth He now call upon, but him that was pained He brings to this one. For because this who hath done the wrong would not easily come to make excuse, out of shame, and confusion of face, He draws that other to him, and not merely so, but in such way as also to correct what hath been done. And He saith not, "Accuse," nor "Charge him," nor "Demand satisfaction, and an account," but, "Tell him of his fault," saith He. For he is held in a kind of stupor through anger and shame with which he is intoxicated; and thou, who art in health, must go thy way to him that is ill, and make the tribunal private, and the remedy such as may be readily received. For to say, "Tell him of his fault," is nothing else than "Remind him of his errors" tell him what thou hast suffered at his hand, which very thing, if it be done as it ought, is the part of one making excuse for him, and drawing him over earnestly to a reconciliation.

If then your brother have sinned against you, or hurt you in any matter, you have power, indeed must needs forgive him, for we are charged to forgive our debtors their debts. But if a man sin against God, it is no longer in our decision. But we do all tho contrary of this; where God is wronged we are merciful, where the affront is to ourselves we prosecute the quarrel. Thy brother is to be reproved in private, lest if once he has lost a sense of shame, he should continue in sin.

(Serm. 82. 1.) Our Lord admonishes us not to overlook one another's faults, yet not so as seeking for matter of blame, but watching what you may amend. For our rebuke should be in love, not eager to wound, but anxious to amend. If you pass it by, you are become worse than he. He by doing you a wrong hath done himself a great hurt; you slight your brother's wound, and are more to blame for your silence than he for his ill words to you. (de Civ. Dei, i. 9.) For often we wrongly shun to teach and admonish, or to rebuke and check the wicked, either because the task is irksome, or because we would escape their enmity, lest they should harm or obstruct us in temporal things, whether in gaining objects we desire, or in holding what our frailty fears to love. But if any one spares reproof of evil doers, because he seeks fitter occasion, or fears to make them worse, or that they may be an impediment to the good and pious living of other weak ones, or may grieve them, or turn them from the faith; herein there is seen no considerations of covetousness, but the prudence of charity. And much weightier reason have they who are set over the churches, to the end they should not spare to rebuke sin; though not even he is free from this blame, who, though not in authority, wots of many things in them to whom he is bound by the ties of this life, which should be touched by admonition or correction, but neglects to do so; shunning their displeasure on account of things which he does not unduly use in this life, but wherewith he is unduly delighted. (Serm. 82, 7.) When any one therefore offends against us, let us be very careful, not for ourselves, for it is glorious to forget an injury; forget therefore your own wrong, but not the wound your brother has sustained; and tell him of his fault between him and you alone, seeking his amendment and sparing his shame. For it may be that out of shame he will seek to defend his fault, and thus you will only harden, while you sought to do him good. (ubi sup.) But the Apostle says, Them that sin 'rebuke before all, that others may fear to do the like. (1 Tim 5:20.) Sometimes therefore your brother is to be spoken to between thee and him alone, sometimes to be rebuked before all. What you must do first, attend and learn; If thy brother, says He, sin against thee, tell him of his fault between thee and him alone. Why? Because he has sinned against you? What is it that he has sinned against you? You know that he has sinned, and therefore since his sin was in private, let your rebuke be in private too. For if you alone know of his trespass, and proceed to rebuke him before all, you do not correct but betray him. Your brother has sinned against you; if you alone know thereof, then he has sinned against you only; but if he did you a wrong in the presence of many, then he has sinned against those also who were witnesses of his fault. Those faults then are to be rebuked before all, that are committed before all; those which are done in private, are to be rebuked in private. Discern times, and the Scriptures are consistent. But why do you correct your neighbour? Because his trespass has hurt yourself? Far be it from thee. If you do it from self-love, you do nought; if you do it from love of him, you do most rightly. Lastly, in what you shall say to him, keep in view for whose sake it is that you ought to do it, for your own or for his, for it follows, If he hear thee, thou hast gained thy brother; do it therefore for his sake, that you may gain him. And do you confess that by your sin against man you were lost; for if you were not lost, how has he gained you? Let none then make light of it when he sins against his brother.

He does not command us to forgive indiscriminately, but him only that will hearken and be obedient, and do penitence; that neither should forgiveness be unattainable, nor sufferance be too far relaxed.