Willful Discipline

"Fasting asserts the will against the appetite - the reward being self-mastery and the danger pride: involuntary hunger subjects appetites and will together to the Divine will, furnishing an occasion for submission and exposing us to the danger of rebellion. But the redemptive effect of suffering lies chiefly in its tendency to reduce the rebel will. Ascetic practices, which in themselves, strengthen the will, are only useful in so far as they enable the will to put its own house (the passions) in order, as a preparation for offering the whole man to God. They are necessary as a means; as an end, they would be abominable, for in substituting will for appetite and there stopping, they would merely exchange the animal self for the diabolical self."

C.S. Lewis, The Problem of Pain p. 100