From Andrew Murray,
Lesson 13 in With Christ in the School of Prayer:
Prayer is the reaching out after God and the unseen; fasting, the letting go of all that is of the seen and temporal. While ordinary Christians imagine that all that is not positively forbidden and sinful is lawful to them, and seek to retain as much as possible of this world, with its property, its literature, its enjoyments, the truly consecrated soul is as the soldier who carries only what he needs for the warfare.