Saint Thomas Aquinas says, "For we fast for three purposes:
(1) to restrain the desires of the flesh;
(2) to raise the mind to contemplate sublime things;
(3) to make satisfaction for our sins."
Obviously we Lutherans would have to adjust number three on that list to make sure we do not confuse giving up a meal or two or even three with the blood of Christ shed in suffering upon the cross. That mistake should not take place but it does and we find ourselves more comfortable thinking of salvation as a business transaction in which we give up something we like for God to give up something He likes (like punishing sinners for their sins). So a little careful language here is probably best. Fasting does help to hit home the one, all sufficient sacrifice of Christ and our own sacrifices in response to His atoning sacrifice are not without merit or purpose to be sure but not as imitation of Christ alone but as acknowledgment of the weakness and fragile state of our sinful existence. Therein lies the missing number four from Aquinas' list. We fast to confront our mortality, our vulnerability, our weakness, and our death.
We require food or we will die. Food is not primarily the indulgence of the flesh in the pleasure of eating but the minimum needed to maintain these bodies already marked for death. If we stop eating, we will die. Fasting does not escape from this but embraces it, confesses it, and admits this hard truth (sort of like ashes to ashes, dust to dust on Ash Wednesday). Aquinas does not promote fasting as a means of showing solidarity with the poor, of carrying the burden of the hungry, or even acknowledging the needs of the needy. Others do, to be sure, but I am not sure that this is a good thing. Lord knows that going without food for a meal or a day is not the same as living in poverty where hunger consumes a person's existence. It would be a sham and a lie to say that because I skipped breakfast this morning, I am showing solidarity with those who have not eaten for days or those who spend the formative part of the day in pursuit of such basic needs as food and water.
We do not fast as an act of righteousness displayed so that others will notice or honor. Jesus has some harsh words to say about that. We fast to acknowledge our weakness, our great need, the poverty of life since the Fall, and the nearness of death to our fragile lives. We acknowledge in such fasting that we do not deserve Jesus but we need Him desperately and without Him we cannot live. His goodness is not the crown of our day but the foundation -- from the mercies new every morning to the mercy of the cross where our Lord dies in the place of guilty, shameful, death marked sinners -- like me!
We ought to fast more. And not because we are fat and lazy and it would be good for us. We ought to contemplate our need, acknowledge our sin, admit our weakness, and confess our fragile lives before the God who is strong enough to fast for us and die for us. If this be the benefit, then fasting will have borne some godly fruit in our lives -- especially in this week we call Holy.