If you are a preacher of Grace, then preach a true, not a fictitious grace; if grace is true, you must bear a true and not a fictitious sin. God does not save people who are only fictitious sinners. Be a sinner and sin boldly, but believe and rejoice in Christ even more boldly. For he is victorious over sin, death, and the world. As long as we are here we have to sin. This life in not the dwelling place of righteousness but, as Peter says, we look for a new heavens and a new earth in which righteousness dwells… . Pray boldly-you too are a mighty sinner.

(Weimar ed. vol. 2, p. 371; Letters I, “Luther’s Works,” American Ed., Vol 48. p. 281- 282) 

In New York they preach about virtually everything; only one thing is not addressed, or is addressed so rarely that I have as yet been unable to hear it, namely, the gospel of Jesus Christ, the cross, sin, and forgiveness, death and life.
Diedrich Bonhoeffer 1930
In this lecture, Bonhoeffer tipped one sacred cow after the other. Having dealt with the idea of Christ as no mere ethicist, he proceeded to explain the similarity of the Christian religion to other religions. Then he came to his main point: the essence of Christianity is not about religion at all, but about the person of Christ…religion was a dead, man-made thing, and at the heart of Christianity was something else entirely - God himself, alive.
Eric Mexaxas, Bonhoeffer: Pastor, Martyr, Prophet, Spy, page 83