The Cost of Discipleship, 1937
https://archive.org/details/DietrichBonhoefferCostOfDisciples
Cheap grace is the grace we bestow on ourselves. Cheap grace is the preaching of forgiveness without requiring repentance, baptism without church discipline, Communion without confession...Cheap grace is grace without discipleship, grace without the cross, grace without Jesus Christ, living and incarnate.
Costly grace is the gospel which must be sought again and again and again, the gift which must be asked for, the door at which a man must knock. Such grace is costly because it calls us to follow, and it is grace because it calls us to follow Jesus Christ. It is costly because it costs a man his life, and it is grace because it gives a man the only true life. It is costly because it condemns sin, and grace because it justifies the sinner. Above all, it is costly because it cost God the life of his Son: 'Ye were bought at a price', and what has cost God much cannot be cheap for us. Above all, it is grace because God did not reckon his Son too dear a price to pay for our life, but delivered him up for us. Costly grace is the Incarnation of God.
The cross is laid on every Christian. The first Christ-suffering which every man must experience is the call to abandon the attachments of this world. It is that dying of the old man which is the result of his encounter with Christ. As we embark upon discipleship we surrender ourselves to Christ in union with his death—we give over our lives to death. Thus it begins; the cross is not the terrible end to an otherwise god-fearing and happy life, but it meets us at the beginning of our communion with Christ. When Christ calls a man, he bids him come and die.