As I write this, I'm listening to John MacArthur give the most beautiful, most comprehensive explanation of church discipline I've ever heard. He's framing it as a great act of love. We know the Good Shepherd goes after that one lost (straying, also?) lamb, but through church discipline, administered according to the Scriptures with compassion, humility (for none of us are without sin), love, and truth, Father allows us to be a part of that act of drawing the wayward lamb to repentance and restoration. He does not simply let His sinning child wander farther from the Savior. That would be cruel.
Why does He let us have a part in the reclaiming and restoring of that person from our faith community? I think it gives each member of the body opportunity to closely examine his own spiritual condition. We're not to exercise church discipline to make ourselves feel self-righteous, for we have no grounds for such arrogance. We're all wretched sinners, even on our best days.
Of course, the one being disciplined may refuse to accept it. The Bible also instructs us on how to respond to that circumstance. Whatever the outcome, we cannot cease to pray.