How did Dietrich Bonhoeffer use the Sermon on the Mount in The Cost of Discipleship?

In his 1937 work The Cost of Discipleship (Nachfolge), Dietrich Bonhoeffer utilized the Sermon on the Mount as a foundational text to challenge the state of contemporary Protestant churches, particularly within the Lutheran tradition.1

Bonhoeffer employed these biblical teachings to launch a sharp critique against what he termed "cheap grace." He argued that the church had reduced the offer of forgiveness to an unlimited, unconditional commodity that functioned as a justification for ethical laxity and moral compromise.1

By contrast, Bonhoeffer interpreted the Sermon on the Mount as a call to "costly grace"—a life of rigorous discipline, obedience, and active discipleship. During this period, his theological stance was closely aligned with pacifism, emphasizing the radical demands of the gospel in opposition to the prevailing nationalistic climate in Germany. Through this study, he sought to restore a sense of serious, committed Christian living that demanded personal sacrifice rather than passive acceptance of grace.1