Being a pastor means a significant portion of my work revolves around the odious task of dealing with someone's sin. Whether I'm preaching about it, counseling through it, praying over it, it seems much of my energies are directed toward this tireless enemy. Through the years, I've found the following truths from God's Word to be repeatedly proven in times of difficult ministry. Consider this my cheat sheet - gathered through study of God's Word and more-or-less successful conversations with others.
How do we (Biblically) deal with someone else's sin?
First, a prerequisite: ...first take the log out of your own eye, and then you will see clearly to take the speck out of your brother's eye. (Mt. 7:5) While sometimes sin is so blatant and immediate that we don't have time for this step, often we know ahead of time about a difficult conversation with a brother or sister. In those cases, it is our necessary and logical duty to search our own hearts using the spotlight of God's Word, to root out and repent of any sins we may be harboring. If we are faithful to take this step, God will do a few things: (1) He will often show us that we share many of the root sins of those we're hoping to confront. (2) He will humble us so that we will approach the other person as a fellow sinner in great need of grace. (3) He will forgive us, preparing us to do the same.
(Here, a side note for other pastors and elders: in matters of church discipline, our session has tried to follow Jesus' command as much as possible. Before we meet with anyone caught in sin or before we pronounce any discipline, we spend time in personal and corporate confession of sin. If you don't yet do this, please consider adding it to the process the next time you need to deal with sin in the congregation.)
Second, a mindset: as we go to others, sweaty palms and all, we must take with us the following attitudes and convictions.
A willingness to be wrong. The one who states his case first seems right, until the other comes and examines him. (Pro. 18:17) It is natural and unavoidable that we will have begun coming to some conclusion before we meet with someone to discuss a problem. But as much as we can, we need to be ready to hear and to be wrong. Approach your brother or sister with lots of questions, seeking to understand the whole situation, agreeing with God's Word that He knows all things but we certainly don't.
A willingness to be implicated. Consider this well-known verse: Fathers, do not provoke your children to anger, but bring them up in the discipline and instruction of the Lord. (Eph. 5:4) Godly parents deal with someone else's sin more frequently than anyone else. The heartache is that, many times, our children's sin will have something to do with our own sin. This past weekend wasn't a banner weekend for our kids. Without getting into unnecessary detail, we had some big issues to work through. But in each of those issues, the reality was that my kids' sins were made easier by my own. I don't have the choice to not deal with their sin, but neither can I ignore my own part. So it is when we deal with anyone else's sin -- you must have a willingness to see what part of the problem you are.
(Elders, when you practice church discipline, take time to consider how you may have failed to disciple this person in whatever area of doctrine or life they've failed.)
A willingness to forgive. ...if he sins against you seven times in the day, and turns to you seven times, saying, 'I repent,' you must forgive him. (Lk. 17:4) While this should be so obvious as to be unnecessary, experience tells me otherwise. Many times we go to others to discuss their sin, we go with a vindictive heart rather than a broken one. We go with the end goal of making someone feel really bad rather than the goal of restoration. And to whatever extent that's the case, we are not participating in God's gracious plan for that person. Let's put it bluntly: if you don't have the sincere desire to forgive the other person or to see them be fully restored to you and others, then stay home and keep your mouth closed.
A willingness to help. Brothers, if anyone is caught in any transgression, you who are spiritual should restore him in a spirit of gentleness. (Gal. 6:1) Every pastor should be sympathetic to this point, because we've all been on the receiving end of a well-meaning rant by a church member aiming to tell us everything wrong with the church or our ministry but without any desire to actually help fix the problem. But we are all often tempted to the same. How often we come to someone, drop a truth-grenade in their lap, say some forgiving words and then go back to our own lives. Rather than aiming at simple honesty or conviction or even forgiveness, our aim can be nothing lower than restoration. And restoration takes time and effort. While you don't need to be the only helper and friend in the process of restoration, you ought to be one of them.
There's much more that could be written, but these few simple guideposts are usually sufficient to help me navigate the difficult waters of dealing with someone's sin. I hope they help you too.