Q. How did the custom of imposing ashes come to be associated with penance?
A. In ancient Jewish culture, covering oneself with dust and ashes (usually accompanied by the wearing of sackcloth) was a customary gesture of intense grief. The dust and ashes symbolized having been brought low, all the way to the ground.
In the Old Testament, for example, Job covered himself in ashes after his children died and he was painfully afflicted with boils (Job 2:8). Mordecai and his fellow Jews put on sackcloth and ashes when they learned that the Persians were planning genocide against them (Esther 4:1–3). Jeremiah warned his people that God would judge them so severely, the women would “put on sackcloth, and roll in ashes” (Jeremiah 6:26).
Grief over sins—one’s own, or those of a whole nation—called for similar symbolic behavior as a sign of repentance. Here the dust and ashes carried the additional meaning of humbling oneself before God, reminding oneself (as the Ash Wednesday liturgy recalls, echoing the words of divine judgment from Genesis 3:19): “You are dust, and to dust you shall return.”
We can note several biblical examples of using ashes this way as a penance. Job covered himself with ashes a second time as an act of self-humiliation: “I despise myself, and repent in dust and ashes” (Job 42:6). The prophet Daniel “sought God by prayer and supplications with fasting and sackcloth and ashes” (Daniel 9:3).
In the New Testament, Jesus declared that if the mighty works He had performed among His contemporaries (which left them unmoved) had been performed in the pagan cities of Tyre and Sidon, the pagans would have “repented … in sackcloth and ashes” (Matthew 11:21).
Given this historical background, we can understand why Catholic liturgical tradition adapted this ancient custom of imposing ashes to signify penance on what thus came to be called Ash Wednesday.