It’s Easter, and here is an Easter piece of music. Miserere mei, Deus is Latin for Have mercy on me, God:

NPR brings out some of the history of this piece:

Composer Gregorio Allegri’s “Miserere” is a piece of choral music so powerful that a 17th-century pope decreed it could be played only during the week leading to Easter—and then only in the Sistine Chapel.