Do not be gloomy while you are being healed. It is absurd not to rejoice in the soul’s health, and rather to sorrow over the change in food and to appear to favor the pleasure of the stomach over the care of the soul. After all, while self-indulgence gratifies the stomach, fasting brings gain to the soul. Be cheerful since the physician has given you sin-destroying medicine. For just as worms breeding in the intestines or children are utterly eradicated by the most pungent medicines, so too, when a fast truly worthy of this designation is introduced into the soul, it kills the sin that lurks deep within.

—St. Basil the Great, On Fasting and Feasts