Everybody sins. Even believers with many years of Bible knowledge and faithful service will sin. It is the condition of fallen humanity which does not leave us until we are translated to glory. However, sin always separates: person from person, and people from God. But it does not have to stay that way because the gospel of God's grace is designed to bring people to repentance so that they can be forgiven and restored to their Maker's service and to each other.
 
Often people are not aware of the hurt they cause to others. Certainly the disciples had little idea of the grief they caused the Lord Jesus on occasions (Matthew 8:23-27). Jesus knew that believers needed to have a method of dealing with sin-separation, so He taught the disciples the need to confront sin in love, looking for recognition of the offence, repentance and the restoration of mutual love.
 
If private discussion failed to move the offender, then one or two others who had also been offended in the same way should add their evidence. If the sinner refused to accept that there was a problem, then it should be made public to the whole congregation – not to accuse but to add further reconciling voices. However, if there was no recognition of the problem, there is no point in any more discussion. Rebellious believers place themselves outside of the fellowship and they should not be comforted (2 Thessalonians 3:14-15). Isolation from fellowship is designed to bring a godly sorrow which leads to repentance and restoration (2 Corinthians 7:8-10).
 
Church discipline is difficult to get right. Most leaders are reluctant to exercise too much authority for fear of being unpopular, although some leaders are harsh rulers of their congregations. Restorative discipline involves a tension between loving somebody who should be respected by the church, and ensuring that he or she recognises the offence of their sin and repents. This teaching from Jesus is vital for churches to be healthy, encouraging people to keep 'short accounts' with each other and with God. Failure to apply loving discipline will lead to a false gospel being received, weak people may be turned away from Christ and the church will become a nesting site for power-hungry predators.