We should confront wrongdoers - to wake them up to their real character, to move them to repair their relationships, or to at least constrain them and protect others from being harmed by them in the future. Notice, however, that all those reasons for confrontation are reasons of love. The best way to love them and the potential victims around them is to confront them in the hope that they will repent, change, and make things right. The desire for vengeance, however, is motivated not by goodwill but by ill will. ...
Only if you first seek inner forgiveness will your confrontation be temperate, wise, and gracious. Only when you have lost the need to see the other person hurt will you have any chance of actually bringing about change, reconciliation, and healing. You have to submit to the costly suffering and death of forgiveness if there is going to be any resurrection.
I like that Keller points out that it is the "you" that must submit not first the person requiring the confrontation. Keller then quotes Dietrich Bonhoeffer from The Cost of Discipleship.
"My brother’s burden which I must bear is not only his outward lot [and circumstance], … but quite literally his sin. And the only way to bear that sin is by forgiving it in the power of the cross of Christ in which [we] now share. Thus the call to follow Christ always means a call to share [in] the work of forgiving men their sins. Forgiveness is the Christlike suffering which it is the Christian’s duty to bear."