The best book I've read so far...The Cost of Discipleship

Bonhoeffer's most famous work is The Cost of Discipleship, first published in 1939. This book is a rigorous exposition and interpretation of the Sermon on the Mount, and Matthew 9:35-10:42. Bonhoeffer's major concern is cheap grace. This is grace that has become so watered down that it no longer resembles the grace of the New Testament, the costly grace of the Gospels.

By the phrase cheap grace, Bonhoeffer means the grace which has brought chaos and destruction; it is the intellectual assent to a doctrine without a real transformation in the sinner's life. It is the justification of the sinner without the works that should accompany the new birth. Bonhoeffer says of cheap grace:

[It] is the preaching of forgiveness without requiring repentance, baptism without church discipline, Communion without confession, absolution without personal confession. Cheap grace is grace without discipleship, grace without the cross, grace without Jesus Christ, living and incarnate.{1}

Real grace, in Bonhoeffer's estimation, is a grace that will cost a man his life. It is the grace made dear by the life of Christ that was sacrificed to purchase man's redemption. Cheap grace arose out of man's desire to be saved, but to do so without becoming a disciple. The doctrinal system of the church with its lists of behavioral codes becomes a substitute for the Living Christ, and this cheapens the meaning of discipleship. The true believer must resist cheap grace and enter the life of active discipleship. Faith can no longer mean sitting still and waiting; the Christian must rise and follow Christ.{2}

It is here that Bonhoeffer makes one of his most enduring claims on the life of the true Christian. He writes that "only he who believes is obedient, and only he who is obedient believes."{3} Men have become soft and complacent in cheap grace and are thus cut off from the discovery of the more costly grace of self-sacrifice and personal debasement. Bonhoeffer believed that the teaching of cheap grace was the ruin of more Christians than any commandment of works.{4}
Discipleship, for Bonhoeffer, means strict adherence to Christ and His commandments. It is also a strict adherence to Christ as the object of our faith. Bonhoeffer discusses this single-minded obedience in chapter three of The Cost of Discipleship. In this chapter, the call of Levi and Peter are used to illustrate the believer's proper response to the call of Christ and the Gospel.{5} The only requirement these men understood was that in each case the call was to rely on Christ's word, and cling to it as offering greater security than all the securities in the world.{6}

In the nineteenth chapter of Matthew's Gospel we have the story of the rich young man who is inquiring about salvation and is told by Christ that he must sell all of his possessions, take up his cross, and follow. Bonhoeffer emphasizes the bewilderment of the disciples who ask the question, "Who then can be saved?"{7} The answer they are given is that it is extremely hard to be saved, but with God all things are possible.