To fast is to force nature. It is to do away with whatever pleases the stomach. Fasting ends lust, roots out bad thoughts, frees one from evil dreams.
Fasting makes for purity of prayer, an enlightened soul, a watchful mind, a deliverance from blindness. Fasting is the door of compunction, humble sighing, joyful contrition, and end to chatter, an occasion for stillness, a custodian of obedience, a lightening of sleep, health of the body, an agent of dispassion, a remission of sins, the gate, indeed the delight of Paradise.
Based on St. John of the Ladder