Bonhoeffer on Freedom and Self-Discipline

If you set out to seek freedom, you must learn before all things mastery over your sense and soul, lest your wayward desirings, lest your undisciplined members lead you now this way, now that way. Chaste be your mind and your body, and subject to you and obedient, serving solely to seek their appointed goal and objective. None learns the secret of freedom save only by way of control. 

- from Ethics