Theophylact of Ohrid

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.