Theophylact of Ohrid — as excerpted in the Catena Aurea on Luke 17:1-2

“Or, He says that there must arise many obstacles to preaching and to the truth, as the Pharisees hindered the preaching of Christ. But some ask, If it needs be that offences should come, why does our Lord rebuke the author of the offences? for it follows, But woe to him through whom they come. For whatsoever necessity engenders is pardonable, or deserving of pardon. But observe, that necessity itself derives its birth from free-will. For our Lord, seeing how men cling to evil, and put forward nothing good, spoke with reference to the consequence of those things which are seen, that offences must needs come; just as if a physician, seeing a man using an unwholesome diet, should say, It is impossible but that such a one should be sick. And therefore to him that causes offences He denounces woe, and threatens punishment, saying, It were better for him that a mill-stone were hanged about his neck, and he cast into the sea, &c.”