"The promise of grace is not to be squandered; it needs to be protected from the godless. There are those who are not worthy of the sanctuary. The proclamation of grace has its limits. Grace may not be proclaimed to anyone who does not recognize or distinguish or desire it. . . . The world upon whom grace is thrust as a bargain will grow tired of it, and it will not only trample upon the Holy, but also will tear apart those who force it upon them. For its own sake, for the sake of the sinner, and for the sake of the community, the Holy is to be protected from cheap surrender. The Gospel is protected by the preaching of repentance which calls sin sin and declares the sinner guilty. The key to loose is protected by the key to bind. The preaching of grace can only be protected by the preaching of repentance."
Dietrich Bonhoeffer, Collected works of Dietrich Bonhoeffer, ed. Edwin H. Robertson, trans. Edwin H. Robinson and John Bowden, vol. 2, The way to freedom: letters, lectures and notes 1935-1939 (New York: Harper and Row, 1966), 151, citing Mt 7:6, as quoted on pp. 292-293 of Bonhoeffer: pastor, martyr, prophet, spy (Nashville, TN: Thomas Nelson, 2010), by Eric Metaxas.
Statements like this were of course coupled with the practice of confession (to, for example, Bethge).