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: You were bought at a price – and what has cost God much cannot be cheap for us. 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.
– Dietrich Bonhoeffer