Ash Wednesday marks the beginning of the Season of Lent. It is a season of penance, reflection, and fasting which prepares us for Christ's Resurrection on Easter Sunday, through which we attain redemption.
Why we receive the ashes
Following the example of the Nine vites, who did penance in sackcloth and ashes, our foreheads are marked with ashes to humble our hearts and reminds us that life passes away on Earth. We remember this when we are told
"Remember, Man is dust, and unto dust you shall return."
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. Later, all Christians, whether public or secret penitents, came to receive ashes out of devotion. In earlier times, the distribution of ashes was followed by a penitential procession.
The ashes are made from the blessed palms used in the Palm Sunday celebration of the previous year. The ashes are christened with Holy Water and are scented by exposure to incense. While the ashes symbolize penance and contrition, they are also a reminder that God is gracious and merciful to those who call on Him with repentant hearts. His Divine mercy is of utmost importance during the season of Lent, and the Church calls on us to seek that mercy during the entire Lenten season with reflection, prayer and penance.
Ashes were used in ancient times to express mourning. Dusting oneself with ashes was the penitent's way of expressing sorrow for sins and faults. An ancient example of one expressing one's penitence is found in Job 42:3–6. Job says to God: "I have heard of thee by the hearing of the ear: but now mine eye seeth thee. Wherefore I abhor myself, and repent in dust and ashes." (vv. 5–6, KJV) The prophet Jeremiah, for example, calls for repentance this way: "O daughter of my people, gird on sackcloth, roll in the ashes" (Jer 6:26). The prophet Daniel recounted pleading to God this way: "I turned to the Lord God, pleading in earnest prayer, with fasting, sackcloth and ashes" (Daniel 9:3). Just prior to the New Testament period, the rebels fighting for Jewish independence, the Maccabees, prepared for battle using ashes: "That day they fasted and wore sackcloth; they sprinkled ashes on their heads and tore their clothes" (1 Maccabees 3:47; see also 4:39).
Other examples are found in several other books of the Bible including, Numbers 19:9, 19:17, Jonah 3:6, Matthew 11:21, and Luke 10:13, and Hebrews 9:13. Ezekiel 9 also speaks of a linen-clad messenger marking the forehead of the city inhabitants that have sorrow over the sins of the people.
It marks the start of a 43-day period which is an allusion to the separation of Jesus in the desert to fast and pray. During this time he was tempted. Matthew 4:1–11, Mark 1:12–13, and Luke 4:1–13. While not specifically instituted in the Bible text, the 40-day period of repentance is also analogous to the 40 days during which Moses repented and fasted in response to the making of the Golden calf.