Discipline is the other side of discipleship. Discipleship without discipline is like waiting to run in the marathon without ever practicing. Discipline without discipleship is like always practicing for the marathon but never participating. It is important, however, to realize that discipline in the spiritual life is not the same as discipline in sports. Discipline in sports is the concentrated effort to master the body so that it can obey the mind better. Discipline in the spiritual life is the concentrated effort to create the space and time where God can become our master and where we can respond freely to God's guidance. Thus, discipline is the creation of boundaries that keep time and space open for God. Solitude requires discipline, worship requires discipline, caring for others requires discipline. They all ask us to set apart time and a place where God's gracious presence can be acknowledged and responded to.
Henri J. M. Nouwen