Jon Walker in his book, In Visible Fellowship: A Contemporary View of Bonhoeffer’s Classic Work:  Life Together writes in chapter 34 about whom do we confess to in the fellowship of the church. Dietrich Bonhoeffer wrote…

Dietrich Bonhoeffer

Anybody who lives beneath the Cross and who has discerned in the Cross of Jesus the utter wickedness of all men and of his own heart will find there is no sin that can ever be alien to him. Anybody who has once been horrified by the dreadfulness of his own sin that nailed Jesus to the Cross will no longer be horrified by even the rankest sins of a brother. 

Walker writes that The Big Idea of the chapter is…

Only those who live under the cross of Jesus can hear confession. And only those who confess can hear the confession of sin.

Walker added:

…Confessing to one another helps us see each other under the Cross of Jesus, where we are judged, yet granted mercy through the blood of Jesus Christ.

The Cross pushes us past our harsh human criticism and weak indulgences toward “the spirit of divine severity and divine love., We enter into the reality of grace–that we need God’s grace because of our sin–an in that reality, we see the death of our sin.

…We hear confession from one another so that each of us in the fellowship can experience this new gladness: “Give me again the joy that comes from your salvation, and make me willing to obey you. Then I will teach sinners your commands, and they will turn back to you.” (Psalm 51:12-13) 

…To be like Jesus…We must be broken and humbled before the Father in order to hear the confession of others…

(Jon WalkerIn Visible Fellowship: A Contemporary View of Bonhoeffer’s Classic Work: Life Together, Chapter 34)