NOTES for Ис 58:1-9
Fasting as a religious practice was known both to Yahwism and to Judaism. However, neither Yahwism nor Judaism knew prolonged fasts like those practiced by medieval Christians. The original meaning of fasting was mourning, usually for a deceased relative, and such a mourning fast generally lasted from one to three days. It was normally a complete fast: those fasting ate and drank nothing from the evening before the fast until the evening of the fast day itself. Entire towns or villages could also undertake a fast in the event of some disaster, especially one known, often from a prophet, to have been allowed by God because of the inhabitants’ sins.
Such fasts, however, were one-time observances, undertaken on each particular occasion. In the post-exilic period, when the religious life of the Jewish people had become unthinkable outside the Synagogue, the practice arose of regular one-day fasts, usually twice a week. These were no longer connected with specific events, for which additional fasts were observed, but were regarded as a kind of spiritual exercise that every believing Jew had a religious duty to perform.
These fasts were supposed to be connected with sins the person fasting might have committed, perhaps even unknowingly. But, as usually happens in such cases, they became a mere formality, a peculiar “sacrifice” to God offered by abstaining from food and water for a full day. Few people thought to ask whether God needed such a fast at all. Abstinence from food and drink was supposed to make the fasting person step out of the ordinary routine of daily life, remember God and his neighbor, and experience anew and vividly what one is inclined to forget amid everyday bustle. In practice, abstinence itself became an element of the daily religious routine, as habitual as the routine itself.
In such a situation, the prophet had to remind those fasting that fasting is not merely a religious duty or a sacrifice to God, who has no need of exercises in abstinence for their own sake, but a way to shift a person’s attention from himself to God and to his neighbors. If a fast does not fulfill this function, God does not need it and it brings no benefit to the person.