Below is the full version of the magnificent “Miserere mei, Deus” composed by the Catholic priest and Roman School composer, Father Gregorio Allegri (c. 1582-1652), and here brilliantly performed by the Choir of New College, Oxford.
The Miserere is Psalm 50 (51), a penitential psalm that is sung daily as the first psalm of schema II in the office of Laudes during penitential seasons. It is very Lenten.
(From DRBO.ORG.) Miserere. The repentance and confession of David after his sin. The fourth penitential psalm.
 Unto the end, a psalm of David,  When Nathan the prophet came to him after he had sinned with Bethsabee.  Have mercy on me, O God, according to thy great mercy. And according to the multitude of thy tender mercies blot out my iniquity.  Wash me yet more from my iniquity, and cleanse me from my sin.  For I know my iniquity, and my sin is always before me. [continued…]
 To thee only have I sinned, and have done evil before thee: that thou mayst be justified in thy words and mayst overcome when thou art judged.  For behold I was conceived in iniquities; and in sins did my mother conceive me.  For behold thou hast loved truth: the uncertain and hidden things of thy wisdom thou hast made manifest to me.  Thou shalt sprinkle me with hyssop, and I shall be cleansed: thou shalt wash me, and I shall be made whiter than snow.  To my hearing thou shalt give joy and gladness: and the bones that have been humbled shall rejoice.
 Turn away thy face from my sins, and blot out all my iniquities.  Create a clean heart in me, O God: and renew a right spirit within my bowels.  Cast me not away from thy face; and take not thy holy spirit from me.  Restore unto me the joy of thy salvation, and strengthen me with a perfect spirit.  I will teach the unjust thy ways: and the wicked shall be converted to thee.
 Deliver me from blood, O God, thou God of my salvation: and my tongue shall extol thy justice.  O Lord, thou wilt open my lips: and my mouth shall declare thy praise.  For if thou hadst desired sacrifice, I would indeed have given it: with burnt offerings thou wilt not be delighted.  A sacrifice to God is an afflicted spirit: a contrite and humbled heart, O God, thou wilt not despise.  Deal favourably, O Lord, in thy good will with Sion; that the walls of Jerusalem may be built up.
 Then shalt thou accept the sacrifice of justice, oblations and whole burnt offerings: then shall they lay calves upon thy altar.