Pie Jesu is the title given to musical settings of the final couplet of the Dies Irae (Day of Wrath), normally a part of the Requiem Mass, a famous thirteenth century Latin hymn thought to be written by Thomas of Celano. The poem describes the day of judgment, the last trumpet summoning souls before the throne of God, where the saved will be delivered and the unsaved cast into eternal flames. The Pie Jesu combines and paraphrases the final verses of the Dies Irae and the Agnus Dei. Pie (the vocative of the word pius) is conventionally translated as "sweet", but normally means "dutiful", "godly" or "kind". Here's the full couplet in the Latin in which it was written (only the first half is heard on this tone, although it is repeated), followed by the translation to English (which is literal): Pie Jesu Domine, dona eis requiem. Dona eis requiem sempiternam. ("O sweet Lord Jesus, grant them rest; grant them everlasting rest."). Whacking your head with the Psalter is optional.
