Shabbat Enjoyment and the Limitations of Social Justice
If we read chapter 58 of Yishayahu in its entirety, we encounter a surprising and even jarring juxtaposition. The beginning of the chapter is a searing admonition not to be hypocritical in serving G- d. The prophet laments how despicable it is that we act with external piety while we oppress the unfortunate. Our fasts are of no interest to HaShem if they are not accompanied by sincere repentance. What HaShem really wants from us is to "untangle the snarls of wickedness, and open the ties of perverted justice; to set free the oppressed and undo the miscarriage of justice"; "to give food to the hungry, and bring the impoverished into your home; if you see the naked then clothe him, and don't neglect your kin".
The chapter then continues with a passage that commands honoring and indulging the Shabbat! No mention whatsoever is made of helping the unfortunate, yet the envisioned reward is similar to the one made in the first part of the chapter!
It seems that our fasts are despicable to G-d if they are not accompanied by social concern; but our "feasts" are acceptable to Him even without such concern!
We find a parallel contrast implicit in a similar admonition of the prophet Malachi. Malachi bewails the fact that the Kohanim in the Temple are bringing the sacrifices in a perfunctory way, without proper awe towards the One to Whom the offerings are brought. HaShem warns them, "Behold, I rebuke you with [shortage of] seed, and I smear excrement on your faces - the excrement of your holidays [Yom Tov offerings]; and it will draw you near to it" (Malachi 2:3).
The Zohar (Yitro II:88b) points out that this exhortation refers specifically to Yom Tov offerings, implying that lack of concern for others is a much greater problem on Yom Tov than it is on Shabbat.
This doesn't mean that Shabbat observance is unrelated to social concern. On the contrary, the Torah repeatedly connects the observance with Shabbat with the message of equality and concern for the needy. For instance, in the passage introducing the manna, which is the first place we encounter the Shabbat, we learn that each person received an equal amount (Shemot 16:18). And on Mount Sinai, HaShem commands us to give rest to our servants on Shabbat "so that your manservant and maidservant should rest like you", so that we should remember that we also were slaves in Egypt until HaShem freed us (Devarim 5:14-15).
However, social concern as a monolithic religious ideal is inherently limited. Consider the paradox of the man who has a respectable job and a comfortable house. Yet despite the fact that he has "everything", he feels a spiritual vacuum, because his life revolves around his own needs. He decides to devote himself to others, and fights for social equality. His minor loss of economic well-being is more than made up for by his newly-acquired sense of mission. What will happen if his quest is successful? Everyone will attain a respectable job and a comfortable house - and everyone will feel the same spiritual emptiness he started with! We see that an exclusive focus on social concern is just a more enlightened form of materialism.
Concern for others is certainly an essential value in Judaism. It is despicable hypocrisy to fast in order to demonstrate that material enjoyments are meaningless to us, if at the same time we rapaciously strive to increase our material well-being at the expense of the downtrodden. This is the theme of the first half of chapter 58 of Yishayahu.
But even after we feed the hungry and clothe the naked, after we free ourselves from obsession with material gain, our material natures remain with us. We cannot fast the year round! We have to find a way for rich and poor alike to maintain their connection to material possessions, but to enjoy these possessions in an elevated way - elevated in the sense of "dignified", and elevated in the sense of "sanctified". This is accomplished through the mitzva of honoring and enjoying Shabbat. In this way we bestow an inner meaning on our accomplishments in social justice, as the prophet Yishayahu concludes in the second half of the chapter.