Fasting is supposed to be the ordinary practice of the godly. Christ does not make light of it, but merely cautions them against its abuses.... It is an appendage to prayer, and designed to aid its importunity. It is humbling, and in a manner, chastising ourselves before God.... The spirit of it is expressed in the following passages--"So do God to me and more also, if I taste bread, or aught else, till the sun be down." "Surely I will not come into the tabernacle of my house, nor go up into my bed; I will not give sleep to mine eyes, nor slumber to mine eyelids, until I find out a place for the Lord, an habitation for the mighty God of Jacob." No mention is made of the time, or how often the duty should be attended to.... It is only a means, however; if rested in as an end, it will be an abomination in the sight of God.

Andrew Fuller, qtd. in John Piper, A Hunger for God, p. 191

"Half of Christian fasting is that our physical appetite is lost because our homesickness for God is so intense. The other half is that our homesickness for God is threatened because our physical appetites are so intense. In the first half, appetite is lost. In the second half, appetite is resisted. In the first, we yield to the higher hunger that is. In the second, we fight for the higher hunger that isn't. 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." (John Piper, A Hunger for God)

We tend to vastly underestimate the importance of our bodies, but they are part of our being. We're not mere spirits who inhabit bodies. We are embodied, incarnated beings who tend not to be driven by our thoughts, but by something more basic — our affections, or even, as James K. A. Smith puts it in Desiring the Kingdom, our gut. I was reminded of this fact as I came across this passage last night in Jerome Jerome's Three Men in a Boat:

How good one feels when one is full — how satisfied with ourselves and with the world! People who have tried it, tell me that a clear conscience makes you very happy and contented; but a full stomach does the business quite as well, and is cheaper, and more easily obtained. One feels so forgiving and generous after a substantial and well-digested meal — so noble-minded, so kindly-hearted.  

It is very strange, this domination of our intellect by our digestive organs. We cannot work, we cannot think, unless our stomach wills so. It dictates to us our emotions, our passions. After eggs and bacon, it says, "Work!" After beefsteak and porter, it says, "Sleep!" After a cup of tea (two spoonsful for each cup, and don't let it stand more than three minutes), it says to the brain, "Now, rise, and show your strength. Be eloquent, and deep, and tender; see, with a clear eye, into Nature and into life; spread your white wings of quivering thought, and soar, a god- like spirit, over the whirling world beneath you, up through long lanes of flaming stars to the gates of eternity!" 

After hot muffins, it says, "Be dull and soulless, like a beast of the field — a brainless animal, with listless eye, unlit by any ray of fancy, or of hope, or fear, or love, or life." And after brandy, taken in sufficient quantity, it says, "Now, come, fool, grin and tumble, that your fellow-men may laugh — drivel in folly, and splutter in senseless sounds, and show what a helpless ninny is poor man whose wit and will are drowned, like kittens, side by side, in half an inch of alcohol." 

We are but the veriest, sorriest slaves of our stomach. Reach not after morality and righteousness, my friends; watch vigilantly your stomach, and diet it with care and judgment. Then virtue and contentment will come and reign within your heart, unsought by any effort of your own; and you will be a good citizen, a loving husband, and a tender father — a noble, pious man.

From Jonathan Edwards's "Advice to Young Converts":

Under special difficulties, or when in great need of or great longings after particular mercies for your self or others, set apart a day of secret fasting and prayer alone. Let the day be spent not only in petitions for the mercies you desired, but in searching your heart, and looking over your past life, and confessing your sins before God, not as practiced in public prayer, but by a very particular rehearsal before God. Include the sins of your past life from your childhood up until now, both before and after conversion, with particular circumstances and aggravations. Also be very particular and as thorough as possible, spreading all  the abominations of your heart before him. 

From A Hunger for God, John Piper, pp. 21-23:

"Bread magnifies Christ in two ways: by being eaten with gratitude for his goodness, and by being forfeited out of hunger for God himself. ... In the heart of the saint both eating and fasting are worship. Both magnify Christ. Both send the heart--grateful and yearning--to the Giver. Each has its appointed place, and each has its danger. The danger of eating is that we fall in love with the gift; the danger of fasting is that we belittle the gift and glory in our willpower."

"Fasting proves the presence, and fans the flame, of that hunger [for God]. It is an intensifier of spiritual desire. It is a faithful enemy of fatal bondage to innocent things. It is the physical exclamation point at the end of the sentence: 'This much, O God, I long for you and for the manifestation of your glory in the world!'"

"If you don't feel strong desires for the manifestation of the glory of God, it is not because you have drunk deeply and are satisfied. It is because you have nibbled so long at the table of the world. Your soul is stuffed with small things, and there is no room for the great. God did not create you for this. There is an appetite for God. And it can be awakened. I invite you to turn from the dulling effects of food and the dangers of idolatry, and to say with some simple fast: 'This much, O God, I want you."

From A Hunger for God by John Piper:

"One of the reasons for fasting is to know what is in us. ... In fasting it will come out. You will see it. And you will have to deal with it or quickly smother it again. When midmorning comes and you want food so badly that the thought of lunch comes as sweet as a summer vacation, then suddenly you realize, "Oh, I forgot, I made a commitment. I can't have that pleasure. I'm fasting for lunch too." Then what are you going to do with all the unhappiness inside? Formerly, you blocked it out with the hope of a tasty lunch. The hope of food gave you the good feelings to balance out the bad feelings. But now the balance is off. You must find another way to deal with it.

At these points we really begin to discover what our spiritual resources are. The things I discover about my soul are so valuable for the fight of faith. . . . What a servant [fasting] is! Humbly and quietly, with scarcely a movement, she brings up out of the dark places of my soul the dissatisfactions in relationships, the frustrations of the ministry, the fears of failure, the emptiness of wasted time. And just when my heart begins to retreat to the delicious hope of eating supper with friends at Pizza Hut, she quietly reminds me: not tonight. It can be a devastating experience at first. Will I find spiritual communion with God sweet enough, and hope in his promises deep enough, not just to cope, but to flourish and rejoice in him? Or will I rationalize my need to fast and retreat to the medication of food? The apostle Paul said, "I will not be mastered by anything" (I Corinthians 6:12). Fasting reveals the measure of food's mastery over us--or television or computers or whatever we submit to again and again to conceal the weakness of our hunger for God."

From Richard Foster's Celebration of Discipline:

"More than any other discipline, fasting reveals the things that control us. . . . We cover up what is inside of us with food and other things. . . . We cover up what is inside us with food and other good things, but in fasting these things surface. If pride controls us, it will be revealed almost immediately. David writes, "I humbled my soul with fasting" (Psalm 69:10). Anger, bitterness, jealousy, strife, fear--if they are within us, they will surface during fasting. At first we will rationalize that our anger is due to our hunger; then we will realize that we are angry because the spirit of anger is within us. We can rejoice in this knowledge because we know that healing is available through the power of Christ." (p. 55).

From Piper's A Hunger for God, pp. 15-19:

"We [must] do anything and go without anything if, by any means, we might protect ourselves from the deadening effects of innocent delights and preserve the sweet longings of our homesickness for God. Not just food, but anything."

Piper paraphrasing Augustine: "We easily deceive ourselves that we love God unless our love is frequently put to the test, and we must show our preferences not merely with words but with sacrifice."

"Many small acts of preferring fellowship with God above food can form a habit of communion and contentment that makes one ready for the ultimate sacrifice. this is one way that fasting serves all our acts of love to God. It keeps the preferring faculty on alert and sharp. It does not let the issue rest. It forces us to ask repeatedly: do I hunger for God? Do I miss him? Do I long for him? Or have I begun to be content with his gifts?"

Some thoughts from John Piper's A Hunger for God, pp. 13-15:

"The birthplace of Christian fasting is homesickness for God."

"My hunger for food was silenced by the hunger of my heart."

"Half of Christian fasting is that our physical appetite is lost because our homesickness for God is so intense. The other half is that our homesickness for God is threatened because our physical appetites are so intense. In the first half, appetite is lost. In the second half, appetite is resisted. In the first, we yield to the higher hunger that is. In the second, we fight for the higher hunger that isn't. 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."

"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."

From Haug & Walker's Journey to the Cross:

"One of the ways we identify with [Jesus'] suffering is by practicing self-denial. Whether it's food or TV or 'me-time,' we deny ourselves particular comforts and pleasures as a way of remembering what he endured. The point is not to manufacture suffering as if we could earn some kind of righteousness through self-denial. Our [purpose] ... is simply to de-clutter our self-absorbed lives."

Jesus did this in the wilderness. He spent forty days eating nothing, preparing His soul for His ministry. The goal of depriving Himself of food was to direct His longings to His Father. Haug & Walker go on:

"'The devil said to him, "If you are the Son of God, command this stone to become bread"' (Luke 4:3). Certainly Jesus could have done this, but the lack of bread revealed a deeper hunger for God, and a deeper satisfaction of being sustained by God."

From Piper's A Hunger for God:

"If you don't feel strong desires for the manifestation of the glory of God, it is not because you have drunk deeply and are satisfied. It is because you have nibbled so long at the table of the world. Your soul is stuffed with small things, and there is no room for the great. God did not create you for this. There is an appetite for God. And it can be awakened. I invite you to turn from the dulling effects of food and the dangers of idolatry, and to say with some simple fast: 'This much, O God, I want you.'"

"We are prone to wander, to pursue life on our terms, to locate our sense of worth and joy and peace outside of God. So the call to repentance is a standing invitation to give up our idolatrous pursuits, and turn to the one true God who restores us to the life for which we were made."

Haug & Walker, Journey to the Cross

On fasting (from not just food, but anything):

"Remember, we give up and take up. When we give up something, we make a clearing in our lives, but unless the clearing is filled up  with light, we stumble around in the dark."

Haug & Walker, Journey to the Cross

"In times of temptation we forget what you have done for us. You give us everything we need, yet we often remain unsatisfied. ... You show us the way we are to follow, yet we often continue on the path of self-indulgence and self-centeredness. Forgive us, we pray. We ask for your direction, your patience, your love, in the name of  Jesus Christ, who, in spite of his temptations, was faithful to your saving Word."

[The Worship Sourcebook]

"This is what Lent is about: joining the company of God's people to consider Jesus' suffering and death; denying ourselves and being sustained by God so that we may run straighter and stronger; gaining hope and strength from the faithfulness of God in Christ Jesus. ... Fix your eyes on Jesus, our brave frontrunner and generous host."

Haug & Walker, Journey to the Cross

"[Don't] miss something that God wants to do in you this season.

Jesus fasted from food and water for forty days in the wilderness. It was not a religious ritual or merely a display of his restraint. Rather, it was a time of trial and temptation which he endured by entrusting himself to God and being nourished on the Word of God. The point of the wilderness, for Jesus, was to experience the real presence of God with him, and power of God at work in him. ...

The ... practice of denying usual comforts is a means of deepening our sense of union with Jesus, and reorienting our life around the things of God. We give up that which distracts and entangles because we want to experience some real joy and freedom in Christ.

Haug & Walker, Journey to the Cross

I am reading Journey to the Cross right now. A blessing so far.

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.

John Piper, A Hunger for God

Half of Christian fasting is that our physical appetite is lost because our homesickness for God is so intense. The other half is that our homesickness for God is threatened because our [other] appetites are so intense. In the first half, appetite is lost. In the second half, appetite is resisted. In the first, we yield to the higher hunger that is. In the second, we fight for the higher hunger that isn't. 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.

John Piper, A Hunger for God