Cheap grace refers to a form of religious indulgence where grace is perceived as something freely given, requiring no commitment or sacrifice on the part of the believer. Bonhoeffer criticizes this concept as it tends to reduce Christianity to a mere intellectual or ritualistic exercise, rather than a transformative faith that requires personal commitment and ethical living. The term serves as a counterpoint to the book’s main theme, “costly grace.”

Costly grace refers to the grace that demands a response, entailing personal sacrifice, moral integrity, and a commitment to following the teachings of Jesus Christ. This term functions as a lens through which Bonhoeffer examines what authentic discipleship entails: the willingness to take up one’s cross and make sacrifices for the sake of one’s beliefs, much like Christ himself.

Discipleship in this work refers to the commitment to follow Jesus Christ both in faith and in action. Bonhoeffer uses the term to explore the depth of commitment required to live out Christian ethics, especially in the face of societal, cultural, or political systems that contradict them. Discipleship, for him, is not a theoretical or merely spiritual endeavor but a tangible, lived experience.