We have already seen that sin is a very serious matter in the eyes of God, and so it must be in ours (Mat 18:1-14). That we must deal radically with sin in our own lives is made evident by Jesus’ hyperbolic language to cut off hand or foot if those body parts are causing us to sin (vv.8-9). But what should we do when a brother, that is, a fellow Christian sins against us?
Jesus addressed this question in Matthew 18:15-20. We must first go to the offending brother and tell him his fault. We must always do this in a spirit of meekness (Gal.6:1). The desired result is reconciliation, or as Jesus put it, gaining your brother. The fractured relationship is restored through seeking and granting forgiveness. But if the offending brother does not hear you, you must pay him another visit taking with you one or two others who will serve as witnesses of your efforts before the church if he does not hear them. If he does not hear the church, you must treat him as an unbeliever. The church’s judgment on this matter is carried out in God’s authority. In fact, the judgment made will have already been made in heaven.
This process can be very difficult, and can lead to the excommunication of the offender (1Cor. 5). We must always proceed in love, desiring to restore not punish the sinning believer. We must not lean on our own understanding in these matters, but obey our Lord’s instructions as laid out in passages like this one and 1Corinthians 5.