1 Corinthians serves as a great snapshot into the personality of the apostle Paul. He's loving...with an edge. The edge is the inverse of the one he carried as a younger man. The blade that persecuted Christians became the blade that held them to the standard. When he found wrongdoing in the church, he couldn't leave well enough alone. With the same intensity that he persecuted the followers of Christ, he now protected their integrity.
I'm thinking a lot of our wide-gate churches and the difficulty in walking some of this out. Let me say that the gate to church used to be incredibly narrow and, in fact, mislocated. We used to invite people in through a gate of rediculous legalism. When they didn't answer the call, we took it as persecution. Somewhere along the line we widened the gate considerably. We decided that we were in no position to judge, so come one, come all. And the came.
Now they're here. They're in the church...and that's good. Unfortunately, they were not asked to declare what was in their bags as they passed through security and some of them are walking around with suitcase bombs of sin. Periodically one of the bags blows up and we have to close an entire concourse.
Paul takes this on in a direct way - chapter five of 1 Corinthians actually talks about the procedure for turning someone out of the church due to unrepentant sin in their life. He points out that we've taken the "who am I to judge" mentality that we should have for the lost and transferred it to one another - we're guilty of gross negligent enablement. 1 Corinthians 5:12,13: What business is it of mine to judge those outside the church? Are you not to judge those inside? God will judge those outside. Expel the wicked man from among you.
The difficulty for us is to walk in grace to the unbeliever and integrity towards the church. There is a standard for those within. To ignore that is to invite disaster on the church and the individual. The same Jesus who described His yoke as easy and His burden as light made a very real point that the way to God is a narrow way and that few would find it.
For the sake of the church - and your brother - don't turn a blind eye to misdoings. The stakes are too high for all of us.