Luke 17:3

After the parable of the rich man who is tormented in punishment, Christ added a commandment to give forgiveness to those who turn themselves from their trespasses, lest any one through despair should not be reclaimed from his fault; and hence it is said, Take heed to yourselves. That there might neither be hard-wrung pardon, nor a too easy forgiveness, neither a harsh upbraiding, to dishearten, nor an overlooking of faults, to invite to sin; therefore it is said in another place, Tell him his fault between him and thee alone. (Mat. 18:15.) For better is a friendly correction, than a quarrelsome accusation. The one strikes shame into a man, the other moves his indignation. He who is admonished will more likely be saved, because he fears to be destroyed. For we more readily give ear to counsel than yield to injury. Fear is a weak preserver of consistency, but shame is an excellent master of duty. For he who fears is restrained, not amended. But He has well said, If he trespass against thee. For it is not the same thing to sin against God and to sin against man.

But we must mark, that He does not bid us forgive every one who sins, but him only who repents of his sins. For by taking this course we may avoid offences, hurting no one, correcting the sinner with a righteous zeal, extending the bowels of mercy to the penitent. By using the number seven He assigns no bound to the giving of pardon, but commands us either to forgive all sins, or always to forgive the penitent. For by seven the whole of any thing or time is frequently represented.

As if He says, Offences must needs come; but it does not follow that you must perish, if only you be on your guard: as it need not that the sheep should perish when the wolf comes, if the shepherd is watching. And since there are great varieties of offenders, (for some are incurable, some are curable,) He therefore adds, If thy brother trespass against thee, rebuke him. But some one may well ask, If when I have several times forgiven my brother he again trespass against me, what must I do with him? In answer therefore to this question He adds, And if he trespass against thee seven times in a day, and seven times in a day turn again to thee, saying, I repent; forgive him.