Thus says the Lord: Cry aloud, and spare not; lift up your voice like a trumpet, and declare to my people their sins, and to the house of Jacob their iniquities. Day by day they seek me, and desire to know my ways; like a people that had done justice, and had not abandoned the judgment of their God, they now ask me for just judgment, and desire to draw near to God, saying, Why have we fasted, and you did not see? Humbled our souls, and you did not know? Because, in the days of your fasts you find your wishes, and all those under your power you goad. If you fast for quarrels and fights, and smite the humble with your fists, why do you fast for me as you do today, for your voice to be heard be heard in your cry? I did not choose this fast, nor a day for a person to humble their soul. Even if you bend down your neck like a ring, and spread under you sackcloth and ashes, you shall not because of this call it an acceptable fast. I did not choose such a fast, says the Lord. But untie every bond of iniquity, unfasten the knots of hard bargains, send the bruised away with remission, and cancel every unjust account. Break your bread for the hungry, and lead the poor who have no shelter into your house: if you see someone naked, clothe them, and you are not to disregard the relations of your own seed. Then your light will break forth as the morning, and your healing speedily spring forth: and your justice will go before you, and the glory of God will surround you. Then you will cry, and God will hear you; while you are still speaking he will say, Behold, I am here. If you remove the bond from yourself, and the stretching out of the hands, and murmuring speech; and if you give bread to the hungry from your soul, and satisfy the humbled soul; then your light will spring up in darkness, and your darkness will be as noon-day: and your God will be with you continually.Shaming words, by which we all stand judged.
(The OSB's helpful gloss: "Fasting and other ascetic acts do not necessarily indicate virtue.")