Manuscripts of the works of the Church Fathers in all languages often contain writings falsely attributed to them for one reason or another. For example, a scholar on Byzantine patristic literature once told me that the works of Pseudo-John Chrysostom considerably outnumber the Saint’s authentic works, which are many and cast. Some of these false attributions result from the mistakes of the medieval monks who made the copies. But medieval people valued originality far less than we do, and in some cases, a mistaken attribution comes from the fact that an authentic passage of a Father’s work was borrowed by someone else, causing the later copyists and editors to assume it was his.
Such appears to be the case with a sermon falsely attributed to St Augustine, part of which is read in the breviary of St Pius V on January 5th, the vigil of the Epiphany, and part today on the feast of the Presentation of the Christ in the Temple, and Purification of the Virgin Mary. In reality, one section of it is taken from an authentic sermon of Augustine, but the larger part, including the two parts read in the breviary, is the work of a monk of the Carolingian era named Ambrosius Autpertus (730 ca. – 784).
Modern scholars have often treated such works as nothing more than frauds and forgeries, and therefore tended to dismiss them as things of no value. Speaking of one of the most famous cases of Patristic pseudonymity, that of St Denys the Areopagite, His Holiness Pope Benedict XVI offered a more benign interpretation. The author who uses another’s name did so “to make an act of humility; he did not want to glorify his own name, he did not want to build a monument to himself with his work but rather truly to serve the Gospel, to create an ecclesial theology, neither individual nor based on himself.” (General Audience, May 14, 2008).
Here is a passage from the sermon in question which, I would say, the Church is fully justified in retaining for liturgical use, even though it is not an authentic work of the Church Father to whom it is attributed.
“O omnipotentia nascentis! o magnificentia de caelo ad terram descendentis! Adhuc in utero portabatur, et ex utero matris a Joanne Baptista salutabatur. In templo praesentabatur, et a Simeone sene famoso, annoso, probato, coronato agnoscebatur. Tunc cognovit, tunc adoravit, tunc dixit: Nunc, Domine, dimittis servum tuum in pace. Differebatur exire de saeculo, ut videret natum, per quem conditum est saeculum. Agnovit Infantem senex, factus est in Puero puer. Innovatus in aetate, qui plenus erat pietate. Simeon senex ferebat Christum infantem, Christus regebat Simeonis senectutem. Dictum ei fuerat a Domino, quod non gustaret mortem, nisi videret Christum Domini natum. Natus est Christus, et impletum est desiderium senis in mundi ipsius senectute. Ipse ad senem hominem venit, qui mundum inveteratum invenit. In isto quidem saeculo diu esse nolebat, et Christum in hoc saeculo videre cupiebat, cantans cum propheta et dicens: Ostende nobis, Domine, misericordiam tuam, et salutare tuum da nobis.
(The Presentation of Christ in the Temple, 1295-1300; mosaic by Pietro Cavallini (1259-1330 ca.) in the apse of the Roman basilica of Santa Maria in Trastevere)

Oh, the omnipotence of Him That is born! Oh, the glory of Him That comes from heaven to earth! While yet He was borne in the womb, He was greeted by John the Baptist. He was presented in the temple, and recognized by the elder Simeon, a famous, ancient, honorable and glorious old man. Then did he know Him, worship Him, and say, ‘Now, o Lord, lettest Thou thy servant depart in peace.’ He put off leaving the world, to see the birth of Him through Whom the world was made. The old man knew the infant; in that boy, he became a boy himself. He was renewed in his years, who was full of devotion. The old man Simeon bore the infant Christ, Christ was the old man Simeon’s Lord. It had been told him by the Lord that he would not taste death before he had seen the birth of the Lord’s anointed. Christ is born, and all the old man’s longing is fulfilled in the last age of the world. He came to an old man, even He who found a decrepit world. He wished not to remain long in the world, and he longed to see Christ in this world, singing with the Prophet, and saying, ‘Show us thy mercy, o Lord, and grant us thy salvation.’ (Psalm 84, 8)”