This is the seventh of the Great Antiphons/O Antiphons sung at the Magnificat at Vespers during the last days of Advent. This antiphon is traditionally used on December 23. (In the Paris Breviary and in medieval English usage it is on December 22.)
O Emmanuel, Rex et legifer noster, exspectatio Gentium, et Salvator earum: veni ad salvandum nos, Domine, Deus noster.
Words: Anonymous, ca. 9th C.
Tune: “O Emmanuel” Gregorian Chant, Mode II, traditional.
This is the English translation of the text as it appears in Fr. Matthew Britt’s 1922 text of The Hymns of the Breviary and Missal:
O Emmanuel, our king and lawgiver, the expectation of all nations and their Saviour: come and save us, O Lord our God.