Why do we begin Lent by receiving ashes?

“The ashes, a symbol of death, help us remember that we shall one day die and that the time for repentance of ours sins is now.”Lent is a time of reflection upon our mortality and our dependence on the merciful love of Jesus Christ for eternal life. Ashes, which are used to mark the foreheads of believers in the form of a cross on Ash Wednesday (the first day of Lent), are a reminder of our mortality.
 
The ashes, a symbol of death, help us remember that we shall one day die and that the time for repentance of ours sins is now. The priest’s words upon the imposition of the ashes – “Remember, man, that thou art dust and unto dust thou shalt return” – echo the words of Christian burial: "Ashes to ashes; dust to dust.”  Furthermore, they are reminiscent of God’s words to Abraham in Genesis 3:19, and Adam’s words: “I am nothing but dust and ashes” (Genesis 18:27). The ashes also remind us that through God’s mercy, we can be converted and experience a rebirth by way of interior conversion.
 
The distribution of ashes began in ancient times. The Old Testament is full of references to the use of ashes a sign of repentance (a few examples can be found in 1 Maccabees 3:47, 2 Samuel 13:19, and Daniel 9:3-6), and the practice continued into the days of the early Church. Christians who had committed serious sins were required to repent publicly, and on Ash Wednesday, the Bishop blessed hair shirts which they were to wear during the forty days of Lent. Ashes made from palms of the previous year’s Palm Sunday were sprinkled on the shirts. Over time, all Christians came to receive ashes out of devotion (this practice has been in place at least since about the eleventh century, having been mentioned in Church documents of 1091 (Cf. Synod of Benventum, 1091 Manse, XX, 739).