Attached here is the most beautiful rendition of the Nunc Dimittis (Latin for "Now Let") that I've heard to date, composed by William Byrd. It's also called Simeon's Song, as it was Simeon who sung it when he met and worshiped the baby Jesus in the temple (Luke 2:22-38). Simeon was also the man who warned Mary that a "sword shall pierce through [her] own soul as well."
You may recognize the translation provided below. In its simpler form, the Nunc Dimittis is part of our liturgy after we've received the Lord's Supper, and it's also part of the final prayers of the day known as Compline. This prayer can certainly lull even a troubled soul to sleep, or at least bring about a sense of peace and calm. Close your eyes and enjoy.
Lord, now lettest thou thy servant depart in peace
according to Thy Word.
For mine eyes have seen Thy salvation, which Thou has prepared
before the face of all people.
A light to lighten the gentiles, and the glory of Your people, Israel.
Nunc dimittis servum tuum, Domine, secundum verbum tuun in pace
Quia viderunt oculi mei salutare tuum.
Quod parasti ante faciem onmium populorum
Lumen ad revalationem gentium, et gloriam plebis tuae Israel.
νῦν ἀπολύεις τὸν δοῦλόν σου, δέσποτα, κατὰ τὸ ῥῆμά σου ἐν εἰρήνῃ·
ὅτι εἶδον οἱ ὀφθαλμοί μου τὸ σωτήριόν σου,
ὃ ἡτοίμασας κατὰ πρόσωπον πάντων τῶν λαῶν,
φῶς εἰς αποκάλυψιν ἐθνῶν καὶ δόξαν λαοῦ σου Ἰσραήλ.