The disciples of Jesus were interested in knowing who is the greatest in the kingdom of heaven (Matt. 18:1). Jesus told them it is the one who humbles himself, and becomes as a little child (Matt. 18:1-4). Furthermore, it is the one who humbly receives the children of God in the name of Christ (Matt. 18:5).
By way of contrast, Jesus warned against those who lay stumbling blocks before His children (Matt. 18:6-7). These are not counted great in the kingdom; just the opposite. Those who do so will lose their souls. To be great in the kingdom one must remove everything that would ensnare one's soul. Repentance is severe, but the judgment against unrepented sins is eternal hell fire (Matt. 18:8-9).
God's constant care for His children is consistent with the reason the Son of Man came to earth; "to save that which was lost" (Matt. 18:10-11). Therefore, rather than despising a brother or sister, especially if he or she has fallen into sin, seek to save this lost sheep (Matt. 18:10, 12-13). God does not want even one of His sheep to be lost (Matt. 18:14).
This introduces the context of Matthew 18:15-17, which explains how those who are "greatest in the kingdom of heaven" will conduct themselves when sinned against by another disciple. The Lord's instruction insures right attitudes and right conduct toward the one who has sinned, while providing situations designed to prompt credibility as well as repentance of sins, so even one soul will not be lost.
Personal Sin to be Addressed Privately
Jesus said, "Moreover if your brother sins against you, go and tell him his fault between you and him alone. If he hears you, you have gained your brother" (Matt. 18:15). The sin under consideration in this verse is personal in nature ("against you"). Its private nature is necessarily implied in the instruction Jesus gives, "go and tell him his fault between you and him alone." The sin is not generally known, and is to be privately discussed. Christ's command also implies the one who sinned may not even know he has sinned against his brother, since Jesus said to "tell him his fault..."
The manner of this initial discussion is informative and persuasive. That is, the sinner needs to "hear" that he has sinned, as well as how to remedy it through repentance (Acts 8:22).
Damage is done when private sins are made public. Gossip, backbiting and rumor-mongering may begin from a failure to keep private sins, private. Remember, the goal is to "seek the one that is straying," not to slay him because he has wandered from the Shepherd (Matt. 18:12).
Identify, Verify and Testify
Jesus continued, "But if he will not hear, take with you one or two more, that 'by the mouth of two or three witnesses every word may be established'" (Matt. 18:16). When the one who committed sin will not repent, the Lord says to follow the directive of Deuteronomy 19:15 (which He quotes), thereby giving another opportunity for both clarity and conversion to occur. The "one or two more" are brought into the conversation with the sinning brother to accomplish at least three things. First, to identify the actual presence of sin. Second, to verify or establish the accuracy of the sinner's refusal to repent. Third, to try to persuade the sinner to repent and turn from his sin. By using this approach, the integrity of the situation is beyond dispute. An allegation of sin must not be allowed to degenerate into name-calling, and one person's word against another person's word. It goes without saying that credible witnesses are required to insure this integrity, since bearing false witness is also a sin (Ephesians 4:25).
Tell it to the Church
Jesus continued, "And if he refuses to hear them, tell it to the church" (Matt. 18:17). If the sinner continues to refuse to be persuaded to repent, it is now time to inform the church of the sinner's failure to repent, so the church can now attempt to save the sinner (Jas. 5:19-20). Each member of the church is to reach out to the erring Christian, attempting to bring him or her back to the Lord's salvation. By taking a united action of trying to save the sinner, the church is being careful not to put a stumbling block before Christ's little one (remember the broader context of this passage, Matthew 18:6-14). Now is the time for each Christian to work to bring the sinner to repentance. That is why a private sin now must be made public to the church. A soul is in danger!
Separation
Jesus concluded, "But if he refuses even to hear the church, let him be to you like a heathen and a tax collector" (Matt. 18:17). If the Christian continues to refuse the church's warnings to repent, a separation must occur. The unrepentant Christian is lost, but he is not the enemy of the church. Like other sinners, he must be admonished about his sin, not encouraged in his sin (2 Thessalonians 3:15). Normal social interaction must be ended, to help produce shame for his sin, and the necessary repentance (2 Thessalonians 3:6, 14). Thus, he is delivered over to Satan to destroy the flesh and, in this final effort, to save his soul. This social separation by each Christian also protects the church from the impure influences of a Christian who has no remorse for continuing to sin against the Lord (1 Corinthians 5:6-13).
Conclusion
Matthew 18:15-17 does not address how to deal with the public sins of Christians. Galatians 2:11-14 and 1 Corinthians 5 give us examples of such public sins, and how to handle them, as we attempt to save the lost and protect the saved. We misapply Matthew 18:15-17 when we demand following its procedure when such public sins occur. This passage is the Lord's prescription for saving souls when personal, private sin takes place. The Lord's teaching is not about getting rid of some one, but about saving the soul of the one who has gone astray (Galatians 6:1-2). When we are approached about sinning against a brother or sister in Christ, may we humbly hear the evidence, and repent of every transgression. And, if we are sinned against, may we follow the Lord's instructions given here, to save one who has gone astray.