Bonhoeffer on the Practice of Spiritual Disciplines

In his exposition of Jesus’ words in  Matthew 6:16-18 in Nachfolge (“Discipleship”), Bonhoeffer has this to say about the importance of practicing spiritual disciplines such as fasting:

Jesus takes for granted that disciples will keep the pious practice or exercise of fasting. The life of a disciple requires the strict practice of austerity. The only purpose of such practices is to make disciples more willing and more joyous in following the designated path and doing the works required of them. The selfish and lethargic will, which resists being of service, is disciplined; the flesh is chastened and punished. The practice of austerity makes me fell the estrangement of my Christian life from the world. A life which remains without any ascetic discipline, which indulges in all the desires of the flesh as long as they are “permitted” by the justitia civilis [civil order], will find it difficult to enter the service of Christ. Satiated flesh is unwilling to pray and is unfit for self-sacrificing service (158)