Luke 17:1

But by the punishment of the man who offends, learn the reward of him who saves. For had not the salvation of one soul been of such exceeding care to Christ, He would not threaten with such a punishment the offender.

Now there are two kinds of offences, of which the one resist the glory of God, but the other serve only to cause a stumbling-block to the brethren. For the inventions of heresies, and every word that is spoken against the truth, are obstructions to the glory of God. Such offences however do not seem to be mentioned here, but rather those which occur between friends and brethren, as strifes, slanders, and the like. Therefore He adds afterwards, If thy brother trespass against thee, rebuke him.

This is spoken according to the custom of the province of Palestine; for among the ancient Jews the punishment of those who were guilty of the greater crimes was that they should be sunk into the deep with a stone tied to them; and in truth it were better for a guilty man to finish his bodily life by a punishment however barbarous, yet temporal, than for his innocent brother to deserve the eternal death of his soul. Now he who can be offended is rightly called a little one; for he who is great, whatsoever he is witness of, and how great soever his sufferings, swerves not from the faith. As far then as we can without sin, we ought to avoid giving offence to our neighbours. But if an offence is taken at the truth, it is better to let the offence be, than that truth should be abandoned.

Because the Pharisees were covetous and railed against Christ when He preached poverty, He put to them the parable of the rich man and Lazarus. Afterwards, in speaking with His disciples concerning the Pharisees, He declares them to be men who caused division, and placed obstacles in the divine way. As it follows; Then said he unto his disciples, It is impossible but that offences will come, that is, hindrances to a good life and which is pleasing to God. 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.