From Dom Guéranger's The Liturgical Year.
Regem venturum Dominum, venite, adoremus.
De Isaia Propheta.
Onus Ægypti. Ecce Dominus ascendet super nubem levem: et ingredietur Ægyptum: et commovebuntur simulacra Ægypti a facie ejus, et cor Ægypti tabescet in medio ejus: et concurrere faciam Ægyptios adversus Ægyptios, et pugnabit vir contra fratrem suum, et vir contra amicum suum, civitas adversus civitatem, regnum adversus regnum.
Come, let us adore the King our Lord, who is to come.
From the Prophet Isaias.
The burden of Egypt. Behold the Lord will ascend upon a light cloud: and will enter into Egypt: and the idols of Egypt shall be moved at his presence, and the heart of Egypt shall melt in the midst thereof: and I will set the Egyptians to fight against the Egyptians, and they shall fight brother against brother, and friend against friend, city against city, kingdom against kingdom.
The Egypt which the Lord is here represented as visiting, and whose idols and empire He will overthrow, is the city of satan, which is to be destroyed, and to give place to the city of God. But how peaceful is the divine Conqueror’s entrance into His conquest! it is on a cloud, a light cloud, that He comes, as on His triumphal chariot. How many mysteries in these few words! ‘There are three clouds,’ says Peter of Blois; 'the first the obscurity of the prophets; the second, the depth of the divine decrees; the third, the prodigy of a Virgin Mother.’ First, as to the obscurity of the prophets, it is essential to every prophecy that it be thus veiled, to the end that man’s free will may not be interfered with; but under this cloud the Lord comes at last, and when the day comes for the prophecy to be accomplished, all things are clear enough. Thus was it with the first coming; so will it be with the second. Then, as to the decrees of God; as they are ordinarily made manifest by second, that is by created, causes only, it almost always happens that the extreme simplicity of the means employed by the divine Wisdom takes men by surprise. Never was this so observable as in the grand event of the Incarnation. Men would naturally expect that, in restoring a fallen world, a power equal, at least, to that which first created it would be displayed; and all they are told about the portent is: ‘You will find the Child wrapped in swaddling clothes, and laid in a manger’! O almighty power of God, how dazzling is Thy light through this cloud! how strong art Thou in this apparent weakness!
But there is the third cloud; it is the Virgin Mary; a light cloud, ‘for,’ says St. Jerome, ‘neither concupiscence, nor the burden of earthly marriage, weighs upon her a cloud, too, laden with a refreshing Dew, since it holds the Just One, who is to be rained down upon us, that our seething passions may be quenched, and the soil of our spiritual life made fertile. How sweet is the majesty of our divine King, when seen thus through this beautiful cloud! O incomparable Virgin! the whole Church of God recognizes thee in that mysterious cloud which the prophet Elias, from the summit of Mount Carmel, saw rising up from the sea, little, at first, like a man’s foot, but sending at last such a plentiful rain that all Israel was refreshed by its abundance. Delay not, we pray thee; give us that heavenly and divine Dew which thou possessest within thee. Our sins have made the heavens as brass, and we are parched; thou alone of creatures art just and pure! Beseech our Lord, who has set up His throne of mercy in thee, to come speedily and destroy our enemies and bring us peace.
Hymn for Advent
(The Mozarabic breviary, first Sunday of Advent)
Cunctorum rex omnipotens,
Mundum salvare veniens,
Formam assumpsit corporis
Qui regnat cum Altissimo,
Virginis intrat uterum,
Nasciturus in corpore,
Mortis vincla disrumpere.
Gentes erant in tenebris:
Videbunt lumen fulgoris,
Cum Salvator advenerit
Redimere quos condidit.
Quem olim vatum praescia
Nunc veniet in gloria,
Nostra ut curet vulnera.
Lætemur nunc in Domino,
Simul in Dei Filio,
Parati eum suscipere
Adventus sui gloria.
The almighty King of the universe,
coming to save the world,
assumed to himself a body
like unto ours.
He who reigns with the Most High,
enters the Virgin’s womb,
that he may be born in the flesh,
and break the bonds of death.
The nations have sat in darkness;
but they shall see the brightest light,
when the Saviout shall come
to redeem his creatures.
He of whom the futureseeing
oracles of the prophets anciently sang,
shall now come in glory
to cure our wounds.
Let us now be glad in the Lord,
and in the Son of God,
and be ready to receive him
in his glorious coming.
Prayer from the Ambrosian Breviary
(Sixth Sunday of Advent, Preface)
Vere dignum et justum est, æquum et salutare: nos tibi, Domine Deus omnipotens, gratias agere: et cum tuæ invocatione virtutis, beatæ Mari» Virginis festa celebrare: de cujus ventre fructus effloruit, qui Panis angelici munere nos replevit. Quod Eva voravit in crimine, Maria restituit in salute. Distat opus serpentis et Virginis. Inde fusa sunt venena discriminis: hinc egressa mysteria Salvatoris. Inde se præbuit tentantis iniquitas: hinc Redemptoris est opitulata majestas. Inde partus occubuit; hinc Conditor resurrexit, a quo humana natura, non jam captiva, sed libera restituitur. Quod Adam perdidit in parente, Christo recepit auctore.
It is truly meet and just, right and available to salvation, that we should give thanks to thee, O Lord God almighty: and that we should, whilst invoking thy power, celebrate the feasts of the blessed Virgin Mary; from whose womb grew tue Fruit, which has filled us with the Bread of angels. That Fruit which Eve took from us when she sinned, Mary has restored to us, and it has saved us. Not as the work of the serpent is the work of Mary. From the one, came the poison of our destruction; from the other, the mysteries of salvation. In the one, we see the malice of the tempter; in the other, the help of the divine Majesty. By the one, came death to the creature; by the other, the resurrection of the Creator, by whom human nature, now not captive but free, is restored; and what it lost by its parent Adam, it regained by its Maker Christ.
 Second Sermon of Advent.
 3 Kings xviii. 42-44.