This is one of the most solemn and discomforting days in the Christian world for we are marked with ashes and made so very much aware of our sin. This day also marks the beginning of forty days of prayer and abstinence leading us to Christ's death and resurrection.
Although the ashen cross we bear today will fade over the hours we can take hope knowing that God's love for us will never fade.
Have mercy upon me, O God, after Thy great goodness; According to the multitude of Thy mercies do away mine offences.Wash me throughly from my wickedness: and cleanse me from my sin.
For I acknowledge my faults: and my sin is ever before me. Against Thee only have I sinned, and done this evil in thy sight: that Thou mightest be justified in Thy saying, and clear when Thou art judged. Behold, I was shapen in wickedness: and in sin hath my mother conceived me. But lo, Thou requirest truth in the inward parts: and shalt make me to understand wisdom secretly.
Thou shalt purge me with hyssop, and I shall be clean: Thou shalt wash me, and I shall be whiter than snow. Thou shalt make me hear of joy and gladness: that the bones which Thou hast broken may rejoice. Turn Thy face from my sins: and put out all my misdeeds.
Make me a clean heart, O God: and renew a right spirit within me.Cast me not away from Thy presence: and take not Thy Holy Spirit from me.O give me the comfort of Thy help again: and stablish me with Thy free Spirit.
Then shall I teach Thy ways unto the wicked: and sinners shall be converted unto Thee. Deliver me from blood-guiltiness, O God, Thou that art the God of my health: and my tongue shall sing of Thy righteousness. Thou shalt open my lips, O Lord: and my mouth shall shew Thy praise. For Thou desirest no sacrifice, else would I give it Thee: but Thou delightest not in burnt-offerings. The sacrifice of God is a troubled spirit: a broken and contrite heart, O God, shalt Thou not despise.
O be favourable and gracious unto Sion: build Thou the walls of Jerusalem.Then shalt Thou be pleased with the sacrifice of righteousness, with the burnt-offerings and oblations: then shall they offer young bullocks upon Thine altar.
English Book of Common Prayer, 1662
Here is Gregorio Allegri's (c.1582 - 1652) Miserere , the famous Latin setting of Psalm 51: