The fasts of the Jews are not true fasts, nor acceptable to God
He says then to them again concerning these things, “Why do you fast to Me as on this day, says the Lord, that your voice should be heard with a cry? I have not chosen this fast, says the Lord, that a man should humble his soul. Nor, though you bend your neck like a ring, and put upon you sackcloth and ashes, will you call it an acceptable fast.” To us He says, “Behold, this is the fast that I have chosen, says the Lord, not that a man should humble his soul, but that he should loose every band of iniquity, untie the fastenings of harsh agreements, restore to liberty them that are bruised, tear in pieces every unjust engagement, feed the hungry with your bread, clothe the naked when you see him, bring the homeless into your house, not despise the humble if you behold him, and not [turn away] from the members of your own family.
Then shall your dawn break forth, and your healing shall quickly spring up, and righteousness shall go forth before you, and the glory of God shall encompass you; and then you shall call, and God shall hear you; while you are yet speaking, He shall say, Behold, I am with you; if you take away from yourself the chain [binding others], and the stretching forth of the hands [to swear falsely], and words of murmuring, and give cheerfully your bread to the hungry, and show compassion to the soul that has been humbled.” To this end, therefore, brethren, He is long-suffering, foreseeing how the people whom He has prepared shall with guilelessness believe in His Beloved. For He revealed all these things to us beforehand, that we should not rush forward as rash acceptors of their laws.
Source: Epistle of Barnabas (New Advent)