Fasting is not very alive and well in the Christian world. Much of that world has long lost any living connection with the historical memory of Christian fasting. It is as though they were Jews who heard there was such a thing as kosher and decided to make up the rules for what to eat and what not to eat because no one knew what was actually kosher.
There are other segments of Christendom who have tiny remnants of the traditional Christian fast, but in the face of a modern world have reduced the tradition to almost meaningless self-sacrifice.
I read recently (though I cannot remember where) that the rejection of Hesychasm was the source of all heresy. In less technical terms we can say that knowing God in truth, participating in His life, union with Him through humility, prayer, love of enemy and repentance before all and for everything, is the purpose of the Christian life. Hesychasm (Greek Hesychia=Silence) is the name applied to the Orthodox tradition of ceaseless prayer and inner stillness.
But these are incorrectly understood if they are separated from knowledge of God and participation in His life, union with Him through humility, prayer, love of enemy and repentance before all and for everything.
And it is the same path of inner knowledge of God (with all its components) that is the proper context of fasting. If we fast but do not forgive our enemies - our fasting is of no use. If we fast and do not find it drawing us into humility - our fasting is of no use. If our fasting does not make us yet more keenly aware of the fact that we are sinful before all and responsible to all then it is of no benefit. If our fasting does not unite us with the life of God - which is meek and lowly - then it is again of no benefit.
Fasting is not dieting. Fasting is not about keeping a Christian kosher. Fasting is about hunger and humility (which is increased as we allow ourselves to become weak). Fasting is about allowing our heart to break.
I have seen greater good accomplished in souls through their failure in the fasting season than in the souls of those who “fasted well.” Publicans enter the kingdom of God before Pharisees pretty much every time.
Why do we fast? Perhaps the more germane question is “why do we eat?” Christ quoted Scripture to the evil one and said, “Man does not live by bread alone but by every word that proceeds from the mouth of God.” We eat as though our life depended on it and it does not. We fast because our life depends on the word of God.
I worked for a couple of years as a hospice chaplain. During that time, daily sitting at the side of the beds of dying patients - I learned a little about how we die. It is a medical fact that many people become “anorexic” before death - that is - they cease to want food. Many times family and even doctors become concerned and force food on a patient who will not survive. Interestingly, it was found that patients who became anorexic had less pain than those who having become anorexic were forced to take food. (None of this is about the psychological anorexia that afflicts many of our youth. That is a tragedy)
It is as though at death our bodies have a wisdom we have lacked for most of our lives. It knows that what it needs is not food - but something deeper. The soul seeks and hungers for the living God. The body and its pain become a distraction. And thus in God’s mercy the distraction is reduced.
Christianity as a religion - as a theoretical system of explanations regarding heaven and hell, reward and punishment, is simply Christianity that has been distorted from its true form. Either we know the living God or we have nothing. Either we eat His flesh and drink His blood or we have no life in us. The rejection of Hesychasm is the source of all heresy.
Why do we fast? We fast so that we may live like a dying man - and in dying we can be born to eternal life.
With fasting I gladden my hope in You, my Lord, Who are to come again.
Fasting hastens my preparation for Your coming, the sole expectation of my days and nights.
Fasting makes my body thinner, so that what remains can more easily shine with the spirit.
While waiting for You, I wish neither to nourish myself with blood nor to take life–so that the animals may sense the joy of my expectation.
But truly, abstaining from food will not save me. Even if I were to eat only the sand from the lake, You would not come to me, unless the fasting penetrated deeper into my soul.
I have come to know through my prayer, that bodily fasting is more a symbol of true fasting, very beneficial for someone who has only just begun to hope in You, and nevertheless very difficult for someone who merely practices it.
Therefore I have brought fasting into my soul to purge her of many impudent fiancé’s and to prepare her for You like a virgin.
And I have brought fasting into my mind, to expel from it all daydreams about worldly matters and to demolish all the air castles, fabricated from those daydreams.
I have brought fasting into my mind, so that it might jettison the world and prepare to receive Your Wisdom.
And I have brought fasting into my heart, so that by means of it my heart might quell all passions and worldly selfishness.
I have brought fasting into my heart, so that heavenly peace might ineffably reign over my heart, when Your stormy Spirit encounters it.
I prescribe fasting for my tongue, to break itself of the habit of idle chatter and to speak reservedly only those words that clear the way for You to come.
And I have imposed fasting on my worries so that it may blow them all away before itself like the wind that blows away the mist, lest they stand like dense fog between me and You, and lest they turn my gaze back to the world.
And fasting has brought into my soul tranquility in the face of uncreated and created realms, and humility towards men and creatures. And it has instilled in me courage, the likes of which I never knew when I was armed with every sort of worldly weapon.
What was my hope before I began to fast except merely another story told by others, which passed from mouth to mouth?
The story told by others about salvation through prayer and fasting became my own.
False fasting accompanies false hope, just as no fasting accompanies hopelessness.
But just as a wheel follows behind a wheel, so true fasting follows true hope.
Help me to fast joyfully and to hope joyously, for You, my Most Joyful Feast, are drawing near to me with Your radiant smile.
From Prayers by the Lake, section 41.