With the coming of Ash Wednesday and the start of Lent, it’s a good time to examine and reflect upon the purpose of the ashes. The following overview comes from the Catholic Online Ash Wednesday explainer:
Ashes are a symbol of penance made sacramental by the blessing of the Church, and they help us develop a spirit of humility and sacrifice. The distribution of ashes comes from a ceremony of ages past. Christians who had committed grave faults performed public penance. On Ash Wednesday, the Bishop blessed the hair shirts which they were to wear during the forty days of penance, and sprinkled over them ashes made from the palms from the previous year. Then, while the faithful recited the Seven Penitential Psalms, the penitents were turned out of the church because of their sins– just as Adam, the first man, was turned out of Paradise because of his disobedience. The penitents did not enter the church again until Maundy Thursday after having won reconciliation by the toil of forty days’ penance and sacramental absolution.
The Upper Room magazine adds to our understanding of the tradition:
Ashes are placed on the forehead, usually in the sign of a cross, in a ritual known as the Imposition of Ashes. As the ashes are placed on the forehead, words such as these are spoken: “Remember that you are dust and to dust you shall return,” recalling God’s words to Adam in Genesis 3:19.