One of the toughest decisions that a church will ever make is to disfellowship or excommunicate someone for a grievous sin. Some are so averse to this procedure that they avoid it altogether, prefering that no accusation of the brethren ever take place. Yet, this is not what Jesus instructed in Matthew 18. In fact he taught us to make the accusation but use appropriate caution, by making sure that before it was brought to the church, there were at least two or three witnesses. The demand for two or three witnesses when an accusation is to be made, was also a safety feature under the Old Testament law.
In verses 18-20 Jesus concluded the topic by stating that where those two or three witnesses would be gathered together, he will be in their midst. In another place, Jesus said that he would never leave us nor forsake us. It is especially comforting for Jesus to emphasize that he will not leave us without his help in times when very grave decisions like this have to be made. A similar statement was made to Peter in chapter 16. In this case, the church has the authority from heaven to either forbid or permit someone to attend church based upon such a gross sin.
What wonderful encouragement in times of such awful decisions! Jesus himself will be there among us to help us make the right decision. He is also concerned for the unrepentant sinner, and will be there in our midst throughout the entire disciplinary process. This does not mean that the decision will therefore be infallible, but that, given the safety measures employed, the best and fairest decision possible will be made.