Christian fasting is not only the spontaneous effect of a superior satisfaction in God; it is also a chosen weapon against every force in the world that would take that satisfaction away.
The greatest enemy of hunger for God is not poison but apple pie. It is not the banquet of the wicked that dulls our appetite for heaven, but endless nibbling at the table of the world. It is not the X-rated video, but the prime-time dribble of triviality we drink in every night. For all the ill that Satan can do, when God describes what keeps us from the banquet table of his love, it is a piece of land, a yoke of oxen, and a wife (Luke 14:18-20). The greatest adversary of love to God is not his enemies but his gifts. And the most deadly appetites are not for the poison of evil, but for the simple pleasures of earth. For when these replace an appetite for God himself, the idolatry is scarcely recognizable, and almost incurable.
Jesus said some people hear the word of God, and a desire for God is awakened in their hearts. But then, “as they go on their way they are choked with worries and riches and pleasures of this life” (Luke 8:14). In another place he said, “The desires for other things enter in and choke the word, and it becomes unfruitful”(Mark 4:19). “The pleasures of this life” and “the desires for other things”—these are not evil in themselves. These are not vices. These are gifts of God. They are your basic meat and potatoes and coffee and gardening and reading and decorating and traveling and investing and TV-watching and Internet-surfing and shopping and exercising and collecting and talking. And all of them can become deadly substitutes for God.
~ John Piper (A Hunger for God, Crossway, 1997).