Isaiah 58 shares the condemnation of hypocritical worship practices found so often in the prophets (for example, Isaiah 1:12-17; Amos 5:21-24; Micah 6:6-8). Jesus, too, was critical of fasting for external reward (Matthew 6:16-18). Proper fasting, says Isaiah, is to loose the bonds of injustice, let the oppressed go free, feed the poor, and clothe the naked. All of this is just what God announced as the mission of Cyrus and the servant in Second Isaiah (42:6-7), and it will be the commission to the speaker of Isaiah 61:1-3. In other words, fasting is not simply a ritual exercise done by an individual for his or her own benefit; by freeing the worshiper from concern for the self, fasting partakes of God's mission of justice and liberation for all people, thus making new both giver and recipient.
The Hebrew text of vv. 10-11 makes clear how this works in its repeated use of the word for "soul" or "self" (Hebrew nefesh): "If you offer your nefesh [your self, your soul] to the hungry and satisfy the nefesh of the afflicted.…The LORD will…satisfy your nefesh in parched places…." In other words, as you pour yourself out for others, you will find yourself--or, as Jesus said, "Those who find their life will lose it, and those who lose their life for my sake will find it" (Matthew 10:39).
The text includes another amazing promise: "You shall cry for help, and [God] will say, Here I am" (v. 9). "Here I am" is the typical and appropriate biblical response of a person called by a superior or by God. In this book, it was Isaiah's response when God commissioned him to be a prophet (see the discussion of Isaiah 6, above). But now, surprisingly, God takes those words of quintessential human response into God's own mouth. Now, God says, "Here I am"--saying, as it were, "I am at your disposal." This happens three times in the latter part of Isaiah (here; 52:6; 65:1), demonstrating the remarkable inclination toward incarnation of God, as portrayed in this material.
6 Is not this the fast that I choose:
to loose the bonds of injustice,
to undo the thongs of the yoke,
to let the oppressed go free,
and to break every yoke?
7 Is it not to share your bread with the hungry,
and bring the homeless poor into your house;
when you see the naked, to cover them,
and not to hide yourself from your own kin?
8 Then your light shall break forth like the dawn,
and your healing shall spring up quickly;
your vindicator* shall go before you,
the glory of the Lord shall be your rearguard.
9 Then you shall call, and the Lord will answer;
you shall cry for help, and he will say, Here I am.
If you remove the yoke from among you,
the pointing of the finger, the speaking of evil,
10 if you offer your food to the hungry
and satisfy the needs of the afflicted,
then your light shall rise in the darkness
and your gloom be like the noonday.
11 The Lord will guide you continually,
and satisfy your needs in parched places,
and make your bones strong;
and you shall be like a watered garden,
like a spring of water,
whose waters never fail.
12 Your ancient ruins shall be rebuilt;
you shall raise up the foundations of many generations;
you shall be called the repairer of the breach,
the restorer of streets to live in.
New Revised Standard Version Bible: Anglicized Edition, copyright © 1989, 1995 National Council of the Churches of Christ in the United States of America. Used by permission. All rights reserved worldwide. http://nrsvbibles.org