“This is the fasting that I wish:
releasing those bound unjustly” (Is 58,6)

The people of Nineveh fasted when Jonah preached repentance to them... Here is what it says: “When God saw by their actions how they turned from their evil way, he repented of the evil that he had threatened to do to them” (Jon 3,10).

It is not said that: “He saw them abstaining on bread and water with
sackcloth and ashes” but that: “They turned back from their evil way and the wickedness of their deeds”. For the king of Nineveh had said: “Every man shall turn from his evil way and from the violence he has in hand” (v.8). This was the real fast and it was accepted...

Because, my friend, when you fast, the best form of abstinence is from wickedness. This is better than abstaining on bread and water, better than “bowing the head like a reed and lying in sackcloth and ashes” as Isaiah says (58,5).

For it is indeed the case that when someone abstains from bread or water or some other form of food, when he puts on sackcloth and ashes and
afflicts himself, he is beloved, beautiful in the eyes of God and acceptable.

What pleases God most is to “undo the chains of impiousness, breaking the bonds deception” (cf. v.6). For such a one “light shall break forth like the dawn and vindication shall march before you. You shall be like a watered garden, like a spring whose water never fails” (v.8,11).

He is not like the hypocrites who “look gloomy” and “neglect their
appearance” so that their fasting may be seen (Mt 6,16).

By Saint Aphrahat (?-c.345), monk and Bishop near Mosul