Isaiah
Chapter 58
Fasting
Cry out aloud for all you are worth; raise your voice like a trumpet blast; tell my people of their offenses, Jacob’s family of their sins.
Is it true that they seek me day after day, longing to know my ways, as a people that does what is right and has not forsaken the word of its God? They want to know the just laws and not to drift away from their God.
“Why are we fasting,” they complain, “and you do not even see it? We are doing penance, and you never notice it.” Look, on your fast days, you push your trade and you oppress your laborers.
Yes, you fast but end up quarreling, striking each other with wicked blows. Fasting as you do will not make your voice heard on high.
Is that the kind of fast that pleases me, just a day to humble oneself? Is fasting merely bowing down one’s head, and making use of sackcloth and ashes? Would you call that fasting, a day acceptable to the Lord?
See the fast that pleases me: breaking the fetters of injustice and unfastening the thongs of the yoke, setting the oppressed free and breaking every yoke.
Fast by sharing your food with the hungry, bring to your house the homeless, clothe the one you see naked and do not turn away from your own kin.
Then will your light break forth as the dawn and your healing comes in a flash. Your righteousness will be your vanguard, the glory of the Lord, your rearguard.
Then you will call, and the Lord will answer, you will cry, and he will say, I am here. If you remove from your midst the yoke, the clenched fist and the wicked word,
if you share your food with the hungry and give relief to the oppressed, then your light will rise in the dark, your night will be like noon.
The Lord will guide you always and give you relief in desert places. He will strengthen your bones; he will make you as a watered garden, like a spring of water whose waters never fail.
Your ancient ruins will be rebuilt, and the age-old foundations will be raised. You will be called the Breach-mender and the Restorer of ruined houses.
The Sabbath
If you stop profaning the Sabbath and doing as you please on the holy day, if you call the Sabbath a day of delight and keep sacred the Lord’s holy day, if you honor it by not going your own way, not doing as you please and not speaking with malice,
then you will find happiness in the Lord, over the heights you will ride triumphantly, and feast joyfully on the inheritance of your father Jacob. The mouth of the Lord has spoken.

Commentaries
Fasting.
This poem highlights the difference between false and proper worship. A perfect liturgical celebration, according to the rubrics, is meaningless if acts of charity toward the disadvantaged do not accompany it. True worship is demonstrated by works of mercy.
The Sabbath.
Observing the Sabbath became the foundation of post-exilic piety.