The Gloria is an ancient hymn of praise to the Trinity that has been in use in the Church since the second century. The opening line of the hymn is taken from Scripture (Lk 2:14), where the angels announce the birth of Christ to the shepherds. The hymn was composed in Greek some time in the second century and can be found recommended as a daily morning prayer in book VII of the Apostolic Constitutions (3rd/4th century). It was introduced to the west by St. Hilary of Poitiers (d 368), who was the first to introduce hymns into the Western Church.
St Hilary was an uncompromising foe of Arianism, a heresy which denied the divinity of Christ and was condemned at the Council of Nicea in 325. St. Hilary’s opposition to Arianism earned himself the title of “Malleus Arianorum”, the Hammer of the Arians, along with the ire of the Arian Emperor Constantius, who exiled him to Phrygia in 356. While St. Hilary was in Phrygia, he was exposed to the hymns in use amongst the eastern Christians of the time. Upon his return home he began to introduce hymns into the western liturgy, borrowing the Gloria from the east, as well as composing some of his own. The hymn has been an integral part of the Mass of the western Rites since the 5th century.
Saint Nicolas, mon amour. (à Saint-Nicolas-du-Chardonnet)