Matthew 18:15

(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. […]

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. […]

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.

And reprove one another, not in anger, but in peace, as ye have it in the Gospel; but to every one that acts amiss against another, let no one speak, nor let him hear aught from you until he repent. But your prayers and alms and all your deeds so do, as ye have it in the Gospel of our Lord.

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. […]