In contradistinction to Roman Catholicism, which defines ecclesiastical communion with the pope as the central mark of the true church, the Protestant Reformers taught that the marks of a true church of Christ are the right preaching of the gospel and the correct administration of the sacraments. Yet, they also added a third mark: the consistent, proper application of church discipline.
Sometimes, the Reformers did not list church discipline as a separate mark of the church. Instead, they subsumed it under the correct administration of the sacraments. That is because church discipline involves determining who has a credible profession of faith and thus can receive the sacraments. Excommunication, the most severe penalty imposed by church elders in church discipline, expels a professing believer from visible church membership and from the Lord’s Supper. In any case, whether we see church discipline as a third mark or as part of the administration of the sacraments, it is certainly right to include it as a defining characteristic of the church.
We see the necessity of church discipline for identifying a true church when we consider the nature of the church. As the called-out people of God, commissioned to walk in holiness (1 Peter 1:13–25), the church must be free of flagrant sin and false teaching if it is to be holy. Failure to deal with erroneous doctrine and scandalous sin allows these contagions to corrupt the entire body. Eventually, the congregation is no longer different from the world, and it is thus no church at all. Engaging in church discipline to encourage repentance keeps the church pure and set apart.
Jesus lays out the basics of church discipline in today’s passage. The first stage is admonishment, with the number of people required to confront a impenitent practitioner of flagrant sin increasing as the confronted person refuses to repent. The second stage of discipline is excommunication (Matt. 18:15–20). But there is a third stage of church discipline not mentioned specifically in Matthew 18—reconciliation and restoration. The final goal of church discipline is not to police everything professing believers say and do, and it is not to be hard on people for the sake of being hard on people. Elders who practice church discipline correctly seek the repentance of the sinner. When disciplined sinners turn from their transgression, they must be restored to the church (2 Cor. 2:5–11).
Church membership vows often include a pledge to safeguard the purity and peace of the church. The most important thing we can do to advance the church’s purity is to pursue holiness ourselves so that we need not come under official church discipline. Let us resolve to practice holiness, to repent of sin, and to encourage one another to follow Christ and His holy way.