Bonhoeffer, Luther & Cheap Grace

For our next book club, I'm reading Dietrich Bonhoeffer's The Cost of Discipleship. In light of Bonhoeffer's historical context (the degeneration of the German confessional church giving way to Nazi control) and our own context (good reformed theology not always have the effect it ought to have), I thought his discussion about the reformer Martin Luther and cheap versus costly grace was fascinating. Here are some interesting quotes that struck me.

The grace which gave itself to [Martin Luther] was a costly grace, and it shattered his whole existence. Once more he must leave his nets and follow. The first time was when he entered the monastery, when he had left everything behind except his pious self. This time even that was taken from him.
...
[Before Luther left the monastery for the secular world] the Christian life had been the achievement of a few choice spirits under the exceptionally favourable conditions of monasticism; now it is a duty laid on every Christian living in the world.
...
The only man who has the right to say that he is justified by grace alone is the man who has left all to follow Christ. Such a man knows that the call to discipleship is a gift of grace, and that the call is inseparable from the grace. But those who try to use this grace as a dispensation from following Christ are simply deceiving themselves.