I’ve noticed in the New Testament that references to “a brother” refers to another Christian. Am I wrong? Are you required to forgive unbelievers when they mistreat you horribly without apology? As I understand things, God cannot forgive me of my daily sins unless I confess them and offer them up in prayer (Earthly Fellowship!). Suppose the pagan doesn’t ever admit (confess) to sinning against you and feels they are justified in their behavior. Can you forgive them for something that isn’t brought into the light by BOTH concerned parties? Time heals all wounds, but what about wounds that keep getting infected with fresh injuries? Also, the dispute resolution process referred to in Mathew 18 would work great for Christians, but what about pagans? And what does it mean to treat a person“as you would a pagan”?
Whether the other person’s a believer or not has nothing to do with it. If someone has wronged us we’re commanded to forgive him or her. The other person’s response is irrelevant to our need to stay in fellowship with God. Otherwise another person could keep you from receiving God’s blessings all your life.
The reconciliation process in Matt. 18:15-17 is meant to be administered between believers. A non-believer would likely not recognize the Church’s authority in settling a dispute. Treating a believer like a pagan or a tax collector (Matt. 18:17) means to have nothing further to do with them. If you’ve done everything you can to reconcile and the other person still isn’t willing, there’s nothing more to do but walk away.
This applies to both believers and non-believers, by the way. There’s nothing in Scripture that requires you to leave yourself open to further mistreatment once you’ve done everything you can to make things right.