Bonhoeffer excludes the idea that knowing about Christ, having an idea or even a well developed systematic theology about Christ and even a general idea about Grace and Forgiveness equals true Discipleship.
Instead, for him Discipleship is where one is ready to follow Christ; no matter what. . .Discipleship is where one will count the cost to live as he calls them to live and in the process of living a new creation is born. Discipleship 59-62
Hence we see simple, hardworking fishermen leave their nets and boats to follow Jesus. This Christmas, what is Christ calling you to leave behind?