From: Luke 17:1-6
On Leading Others Astray, Fraternal Correction
 And He (Jesus) said to His disciples, "Temptations to sin are sure to come; but woe to him by whom they come!  It would be better for him if a millstone were hung around his neck and he were cast into the sea, than that he should cause one of these little ones to sin.  Take heed yourselves; if your brother sins, rebuke him, and if he repents, forgive him;  and if he sins against you seven times in the day, and turns to you seven times, and says, `I repent,' you must forgive him."
The Power of Faith
 The apostles said to the Lord, "Increase our faith!  And the Lord said, "If you had faith as a grain of mustard seed, you could say to this sycamine tree, `Be rooted up, and be planted in the sea', and it would obey you."
1-3. Our Lord condemns scandal, that is, "any saying, action or omission which constitute for another an occasion of sin" ("St. Pius X Catechism", 417). Jesus is teaching two things here: the first is that scandal will "in fact" happen; the second, that it is a grave sin, as shown by the punishment it earns.
The reason why it is so serious a sin is that it "tends to destroy God's greatest work, that of Redemption, through souls being lost; it kills one's neighbor's soul by taking away the life of grace, which is more precious than the life of the body, and it is the cause of a multitude of sins. This is why God threatens with the most severe punishment those who cause others to stumble" ("ibid"., 418). See [the notes on] Matthew 18:6-7; 18-8; 18:10.
"Take heed to yourselves": a serious warning, meaning that we should not be a cause of scandal to others nor should we be influenced by the bad example others give us.
People who enjoy authority of any kind (parents, teachers, politicians, writers, artists, etc.) can more easily be a cause of scandal. We need to be on the alert in this respect in view of our Lord's warning, "Take heed to yourselves."
2. Millstones were circular in shape with a large hole in the center. Our Lord's description, therefore, was very graphic: it meant that the person's head just fitted through the hole and then he could not get the stone off.
3-4. In order to be a Christian one must always, genuinely, forgive others. Also, one has to correct an erring brother to help him change his behavior. But fraternal correction should always be done in a very refined way, full of charity; otherwise we would humiliate the person who has committed the fault, whereas we should not humiliate him but help him to be better.
Forgiving offenses--which is something we should always do--should not be confused with giving up rights which have been justly violated. One can claim rights without any kind of hatred being implied; and sometimes charity and justice require us to exercise our rights. "Let's not confuse the rights of the office you hold with your rights as a person. The former can never be waived" ([St] . Escriva, "The Way", 407).
Sincere forgiveness leads us to forget the particular offense and to extend the hand of friendship, which in turn helps the offender to repent.
The Christian vocation is a calling to holiness, but one of its essential requirements is that we show apostolic concern for the spiritual welfare of others: Christianity cannot be practiced in an isolated, selfish way. Thus, "if any one among you wanders from the truth and some one brings him back, let him know that whoever brings back a sinner from the error of his way will save his soul from death and will cover a multitude of sins" (James 5:20).
5. "Increase our faith!": a good ejaculatory prayer for every Christian. "Omnia possibilia sunt credenti". Everything is possible for anyone who has faith.' The words are Christ's. How is it that you don't say to Him with the Apostles: `"adauge nobis fidem"! increase my faith!'?" ("The Way", 588).
Source: "The Navarre Bible: Text and Commentaries". Biblical text taken from the Revised Standard Version and New Vulgate. Commentaries made by members of the Faculty of Theology of the University of Navarre, Spain. Published by Four Courts Press, Kill Lane, Blackrock, Co. Dublin, Ireland. Reprinted with permission from Four Courts Press and Scepter Publishers, the U.S. publisher.