Matthew 18:6-9
6 But whoso shall offend one of these little ones which believe in me, it were better for him that a millstone were hanged about his neck, and that he were drowned in the depth of the sea.
7 Woe unto the world because of offences! for it must needs be that offences come; but woe to that man by whom the offence cometh!
8 Wherefore if thy hand or thy foot offend thee, cut them off, and cast them from thee: it is better for thee to enter into life halt or maimed, rather than having two hands or two feet to be cast into everlasting fire.
9 And if thine eye offend thee, pluck it out, and cast it from thee: it is better for thee to enter into life with one eye, rather than having two eyes to be cast into hell fire.
The Grace New Testament Commentary - Matthew 18:6-9
18:6-7 Here Jesus is warning against causing "one of these little ones who believe in Me" to fall into sin (skandalizō, "to trip or cause to stumble"). There is something perverse about placing a stumbling stone in front of an unsuspecting or vulnerable child so they might fall. Those who do such things will face severe punishment. "It would be better" to have "a millstone" (a huge wheel-shaped stone used to grind grain) attached as a weight to one's body and sink quickly to the bottom "of the sea" than to commit such an offense.
Jesus is speaking here of children who believe in Him! Despite what some may suggest, believing in Jesus is not limited to adults. Children can and do believe in Him. God's judgment is expressed in Jesus' double use of the word woe. For the world, offenses are inevitable and so is the judgment against those who are responsible for them.
18:8-9 Jesus counsels the listeners to eliminate whatever "causes [them] to sin," whether a "hand or foot," or an eye. If one is in danger of going to hell because of what he might do, then he should cut off his feet and hands. If one is in danger of hell because of what he looks on, he should pluck out his eye. "To enter into life lame or maimed" is better than being "cast into hell fire" with one's whole body intact.
This enigmatic saying is hyperbolic and hypothetical. If drastic measures could be taken, such as dismemberment, to keep one from sinning, it would be worth it. Self-mutilation and dismemberment would not save them, of course, for the problem is in the heart (Matthew 15:8-9, 18-20). However, Jesus assumes for the sake of argument that their trust in external restraint from evil would be sufficient to save. The complete uselessness of such an exercise is plain. That they would trust in externals reveals that those to whom Jesus directs His remarks are unbelievers. Jesus' words are provocative and enigmatic, causing one to think and feel more deeply.
(Editor's note: Another view is that the Lord was suggesting that any hindrance to faith in Him should be eliminated. The hand, foot, and eye suggest what a person does, where he goes, and what he gazes on. While the only condition of eternal life is faith in Christ, a person who keeps himself away from the message about Jesus and is distracted by various friends and pursuits is unlikely to come to faith. Better to eliminate hindrances that keep one from hearing the saving message than to go through life with one's comfortable status quo and end up in hell.)
Charles Bing - Grace, Salvation, and Discipleship - Plucking Out Your Eye, Matthew 5:29-30 (cf. Matthew 18:6-9, Mark 9:43-48)
(Salvation) Interpretation: A person who does not do what is necessary to stop sinning will be thrown into hell.
(Discipleship) Interpretation: It is better to be a believer who suffers loss in order to stop sinning than to be a whole unbeliever thrown into hell.
We remember that Jesus is addressing His disciples with the multitude listening in. He is not telling His disciples that if they continue to sin they will lose their salvation. He is certainly not suggesting if people stop sinning they will avoid hell. He is telling his disciples that kingdom conduct demands a radical effort to avoid a serious sin like the sin of adultery that He mentions (vv. 27-28). Of course, plucking out the eye and cutting off the hand are metaphors for a radical commitment to not sin. While the disciple will have to suffer severely in order to deny his sinful desires, he is better off than an unsaved person who sins with abandon, makes no effort to avoid sin, and remains a whole person (with all his body parts), but is thrown into hell. While cutting off body parts is symbolic, the reality behind the metaphor can involve things like suffering a financial loss to avoid sin, suffering a severed relationship, or suffering a relocation to avoid a temptation. The loss is real and may be painful, but it is nothing compared to those who refuse to deal with their sin and end up in hell.
Mark 9:43-48 uses the same metaphors (but includes cutting off a foot) and the same consequences. In this context, Jesus is teaching his disciples a lesson about greatness in the anticipated kingdom (Mark 9:33-35). Greatness is found in those disciples who value, accept, and serve those who are younger, weaker, and less committed to Christ (the children of Mark 9:36-37 and the one who is not following Christ as a committed disciple, vv. 38-41). Together, these are the "little ones" or the young and immature believers of verse 42. It is a serious offense to the Lord to cause one of these to sin, and therefore wreck their fragile faith, as is shown by the reference to hanging a millstone around the offender's neck and throwing him into the sea.
In verse 43, there is a dramatic shift from talking about someone who causes a little one to sin to directly addressing the disciples' potential to sin. This is probably because a disciple who sins can lead a less mature believer to sin also. As disciples, suffering a temporary loss (if we continue with the metaphor, all body parts would be restored in eternity) and entering life is a better fate than an unbeliever who suffers no loss as he indulges in sin and goes to hell with all his body parts, a whole person (vv. 43-48). Disciples shouldn't grieve about losses in this life when they sacrifice desires for the sake of others, because enduring such a brief loss is nothing compared to the fate of an unbeliever. Worse, the sin of an indulgent unbeliever may cause a little one to sin, bringing the severe punishment represented by the millstone and watery fate.
As followers of Christ, we have a kingdom responsibility to take drastic measures to avoid sin. Sin misrepresents the Lord, despises His grace, and can cause less mature believers to sin, injuring their walk with the Lord. The Lord takes sin seriously, and so should we.