On one occasion, the chief priests and elders approached Jesus while he was teaching and asked him, “By what authority are You doing these things, and who gave You this authority?” (Matt 21:23). While it is obvious that the priests and elders were disputing rather than making careful inquiry, the question they asked is good and deserves being asked and answered. Many indeed ask by what authority does the church practice church discipline? In answering this question, I will seek to briefly demonstrate that we not only practice church discipline because of explicit commands to do so (Matt 18:15–20; Rom 16:17–18; 1 Cor 5:1–13; 1 Tim 1:19–20; 2 Thess 3:6–15), but also because church discipline is inextricably related to the gospel, evangelism, and the Great Commission.
We see this relationship definitionally. Church discipline encompasses both individual and corporate actions of a local church seeking restoration of one of her members as well as the preservation of the assembly’s fellowship of holiness, public testimony, and doctrinal purity. Additionally, the purpose of maintaining a conducive atmosphere for following Christ and experiencing his presence and power is paramount.
For clarity, I distinguish between church discipline and formal church discipline. The former refers to the full breadth of New Testament teaching regarding church discipline, whereas the latter refers to steps that potentially lead to the final removal of an unrepentant member. When church discipline is mentioned, it is the latter that most commonly comes to mind, but the New Testament teaching on church discipline is much more comprehensive. Similarly, church discipline is often understood and supported only if it has the exclusive purpose of redemption for the wayward member. Consequently, it is valued only for its utility in winning a wayward brother or sister. Accordingly, if church discipline does not potentiate such or fails to achieve this goal, it is deemed unworthy of implementation or, if implemented, to have failed.
However, in consideration of the full New Testament teaching on church discipline, one readily sees that it is much more inclusive and actually pervades the life of the church. Properly understood, church discipline seeks redemption, correction, protection, purification, and justice. Consequently, while it is for the sake of seeking redemption of the wayward member, it is also for the sake of the gospel. The lack of church discipline hinders the church from being able to fully live and spread the gospel according to the mandate of Christ. The absence of church discipline leaves the church weakened by the sin of the unrepentant (1 Cor 5:6; 11:17–22; 11:30–32). For that reason, in addition to the redemptive aspect that applies to the wayward member, church discipline is essential for the church to maintain a conducive atmosphere for body life and be effectively redemptive toward the lost as well.
Briefly, the corrective aspect includes such important ministries as prayer, teaching, discipling, counseling, and preaching. These provide instruction and correction for training in righteousness for those who desire to follow Christ. The purity aspect focuses upon the purity of the body (1 Cor 5:6). The church is to be a holy place that is morally and spiritually set apart unto God (1 Pet 1:13–16). Similar to the purity aspect, the protective aspect emphasizes the need to protect the spiritual purity of the fellowship, doctrines, and mission of the church (Rom 16:17–18; 1 Cor 5:1–13; 1 Tim 1:19–20; Eph 4:11–16).
The final aspect is that of justice. Church discipline underscores the sinfulness of sin and keeps before the congregation and the world the reality that sin is a violation of holy righteousness and justice, which a holy God will judge. It stresses that sin is not a psychological dysfunction, sickness, social construct, or mistake without accountability; rather that sin urgently requires one to repent. It testifies that unrepentance is not to be taken lightly, and it is a very serious reminder that if the sinner fails to seek forgiveness by grace and repentance through faith (Eph 2:8–9), he will ultimately be judged by God and find himself eternally separated from God in hell (Rev 21:7–8).
Church discipline highlights the reality that God will judge every violation of justice, as is so graphically demonstrated in Christ’s death on the cross. The availability of forgiveness through repentance emphasizes God’s love that provides an escape from our condign punishment through faith in his Son who died for our sin, bearing the wrath of a holy God. The benefit of the gospel is given to all who repent and believe (John 3:16), but the unrepentant will suffer his just desert, as is seen in the practice of church discipline (1 Cor 5:5; Gal 6:1–5).
The reality of church discipline is that it is not the sin per se that results in formal church discipline, but rather it is the lack of repentance, which is the same standard for eternal judgment. The Bible is clear that unrepented of sin is never excused, overlooked, or forgiven, and it is equally lucid that every sin can be forgiven by repentance and faith in Christ (Luke 13:3; Rom 10:9–10; 2 Pet 3:9). That is the gospel. Correspondingly, we see that church discipline, properly defined, elevates both the seriousness of sin and the wonder of grace, and therefore, the gospel (Heb 2:9; 10:10, 14).
As a result, it is clear that church discipline encompasses redemption for the wayward sinner, protects the church from the moral and spiritual corruption that undermines its effectiveness in spreading the gospel, and combats the world’s constant redefining of sin whether by psychologizing, medicalizing, or reducing it to an inconsequential mistake. Church discipline encompasses redemptive measures for the wayward member, but it is not reducible to that one component because it is equally important for the protection of the church members who are seeking to obey Christ as well as for the lost world who needs to see the church of the Lord Jesus as he designed her to be.
 For a fuller explanation of each of these components see my book, Undermining the Gospel: The Case and Guide for Church Discipline (Bloomington, IN: WestBow Press, 2015).