NOTES for Isa 58:5
The question of fasting is one of the main ones for many Christians. However, Christians are not original here: it was also one of the central questions for Jews, and had been for quite a long time, several centuries before the coming of the Messiah. Why, then, did it occupy such an important place in Jewish life? Originally in Yahwism, fasts were not given nearly so much attention. Yes, of course, on days of mourning, personal or public, a fast was observed, and observed strictly. Jewish fasts were usually complete; people abstained from food and water for the whole day. If the fast lasted many days, which happened infrequently, one could eat and drink only after sunset.
But already in the post-exilic period a practice of regular one-day fasts developed in the synagogue environment, and it lasted at least until the end of the Second Temple period. This practice was followed also by members of the Pharisaic brotherhood. Apparently, in the Gospel era there were two such regular fasts a week. It was assumed that on these days everyone fasted while remembering his own sins. If this had really been so, such a fast could have brought undoubted spiritual benefit.
The same, incidentally, is true of church fasts, whose meaning in the final analysis also comes down either to remembrance of one's own sins or to remembrance of the Savior's death on the cross and of Judas's betrayal. But even before Christ's coming, something happened that completely distorted the essence and meaning of a fast for sins: it turned into a religious obligation. In the course of time much the same happened with our Christian fasts too, despite the Savior's corresponding warnings.
Judging by Isaiah's words, one can think that this transformation began quite early, soon after the Jews returned to Judea after the Babylonian exile, if not earlier. Fasting begins to be perceived as a certain self-limitation valuable in itself, as a kind of punishment of oneself for committed sins. It is assumed that God needs all this, and that the person who acts this way accordingly becomes closer to God and more pleasing to Him. Later a pious myth also arose that fasting supposedly cleanses a person from sin or from its consequences.
All this, of course, was quite far from reality. It goes without saying that no person can cleanse himself from sin. Such cleansing requires God's direct intervention, His direct action. And self-limitation as such has no special benefit for spiritual life. God does not need it. Any self-limitation is valuable only insofar as it allows a person to understand himself, to see the true motives of his actions, to see his sins, and to understand how to resist them.
But even here self-limitation alone is not enough: like any spiritual work, this work presupposes God's participation, without which no self-limitation in itself will reveal anything useful to a person. Yet religious consciousness tends to absolutize the significance of fasting in itself. All the more so because the difference between those who fast and those who do not becomes one of the signs of belonging to a religious community.
Then fasting, having become an end in itself, begins to disorient a person and destroy his spiritual life. It forces him to spend strength and time on what from a spiritual point of view gives him nothing. And sometimes it even brings harm: many religious people begin to take pride in their fasts, wondering that God does not notice their efforts. And they become all the more confirmed in their own rightness the greater the successes they achieve in this peculiar religious sport. Only the reward for the winner in this contest is not the Kingdom, but a feeling of deep religious satisfaction. And that is a poor substitute for the Kingdom.