When it is said
At Matins the reader prays it three times, just before the six psalms that begin the service.
Before the Divine Liturgy begins, the priest and deacon stand at the altar and pray it to themselves twice.
It is also the first line of the Great Doxology, the hymn of praise near the end of Matins.
Where it comes from
Author known
The night at Bethlehem
Near Bethlehem, shepherds were keeping watch over their flock at night when an angel came to them. He told them that a Savior had been born, Christ the Lord, and that they would find the baby lying in a manger. Then a great company of angels appeared with him, praising God in these words (Luke 2:8-14). The shepherds went and found the Child, and went home glorifying and praising God (Luke 2:20).
Sung again at Christmas
The Church retells that night in its own Christmas hymns. The canon of Christmas Matins is credited to the hymn writer St Cosmas, about AD 760. In its seventh song the hosts of heaven cry aloud at the angel’s word, “Glory to God in the highest, and on earth peace, good will toward men; Christ hath shone forth”.
What the words mean
“Good will toward men” or “on whom His favor rests”?
The Greek texts of Luke differ here by one letter. The Byzantine text of the Gospels has eudokia, “good will”, and so does the Great Doxology in the Church’s services. Scholarly editions such as the SBL Greek New Testament have eudokias, which makes the line mean peace among those with whom God is pleased. The Berean Standard Bible follows that reading: “peace to men on whom His favor rests” (Luke 2:14).
The SBL Greek New Testament, Luke 2:14, with its notes; The Great Doxology in Greek, on Greek Wikisource
The Scripture in it
And suddenly there appeared with the angel a great multitude of the heavenly host, praising God and saying: “Glory to God in the highest, and on earth peace to men on whom His favor rests!”
Bible text: Berean Standard Bible, public domain.
In Greek
Δόξα ἐν ὑψίστοις Θεῷ
καὶ ἐπὶ γῆς εἰρήνη,
ἐν ἀνθρώποις εὐδοκία.
From Luke’s Gospel in Greek (2:14), on Elpenor (ellopos.net).