From Dom Guéranger's The Liturgical Year.

O Rex gloriæ, Domine virtutum, qui triumphator hodie super omnes cœlos ascendisti, ne derelinquas nos orphanos; sed mitte promissum Patris in nos, Spiritum veritatis, alleluia.
O King of glory, Lord of hosts, who didst this day ascend in triumph above all the heavens! leave us not orphans, but send upon us the Spirit of truth, promised by the Father, alleluia.

The feast of the Ascension shows us the work of God in its completion. Hence it is that the Church, in her daily offering of the holy sacrifice, thus addresses the eternal Father: the words occur immediately after the consecration, and contain the motives of her confidence in the divine mercy: ‘Wherefore, O Lord, we Thy servants, as also Thy holy people, calling to mind the blessed Passion of Christ Thy Son our Lord, His Resurrection from the dead, and His admirable Ascension into heaven, offer unto Thy most excellent Majesty a pure, holy, and unspotted Host.’ It is not enough for man to hope in the merits of his Redeemer’s Passion, which cleansed him from his sins; it is not enough for him to add to the commemoration of the Passion that of the Resurrection, whereby our Redeemer conquered death; man is not saved, he is not reinstated, except by uniting these two mysteries with a third: the Ascension of the same Jesus who was crucified and rose again. During the forty days of His glorified life on earth, Jesus was still an exile; and, like Him, we also are exiles until such time as the gate of heaven, which has been closed for four thousand years, shall be thrown open, both for Him and for us.

God, in His infinite goodness, made man for a nobler end than that of being mere lord of creation; He gave him a higher destiny than that of knowing such truths as his natural powers could grasp, and of practising virtues that were within the reach of his moral capabilities, and of paying to his Creator an imperfect worship. In His omnipotence and love, He gave to this frail creature an end far above his nature. Though inferior to the angel, and uniting in himself the two natures of matter and spirit, man was created to the same end as the angel. Both were to dwell for eternity in heaven; both were to be eternally happy in the face-to-face vision of God, that is, in the closest union with the sovereign Good. Grace—that wondrous and divine power—was to fit them for the supernatural end prepared for them by the gratuitous goodness of their Creator. This was the design which God had decreed from all eternity: to raise up to Himself these creatures that He had drawn out of nothingness, and to enrich them, agreeably to their sublime destiny, with the treasures of His love and His light.

We know the history of the fallen angels. They revolted against the commandment given them by God as a test of their fidelity, and as a condition of their being admitted into eternal happiness. Rebels were found in each of the choirs. They fell; but the fall and its punishment were personal, and injured none but the actual transgressors. The angels who remained faithful were at once rewarded with the beatific vision and possession of the sovereign Good. Thus did God vouchsafe to make created beings partake in His own infinite happiness: the first elect were the good angels of the nine choirs.

Man was created after the angels; he too fell, and his sin severed the link which united him with God. The human race was, at that time, represented by one man and woman; when they fell, all fell. The gate of heaven was then shut against mankind, for the fall of Adam and Eve implicated us their children; neither could they transmit to us an inheritance which they themselves had lost. Instead of a quick and happy passage through this world, and then a glorious ascension into heaven, we were to have a life short indeed but full of misery, a grave, and corruption. As to our soul, even had she aspired to the supernatural happiness for which she was created, she could never have attained to it. Man had preferred earth for his portion, and the earth was given to him; but this only for a few short years, after which others would take his place, disappear in their turn, and so on to the end, as long as it should please God to perpetuate this fallen portion of His creation.

Yes, it is thus we deserved to be treated; but our merciful Creator had compassion upon us. He hated sin; but He had created us that He might make us partakers of His own glory, and He would not have His design frustrated. The earth was not to be an abode for man to be merely born, live a few days, and then die. When the fulness of time should come, there was to appear in the world a Man, not indeed the first of a new creation, but one like ourselves and of our own race, or, as the apostle expresses it, ‘made of a woman.’[1] This Man, who was to be heavenly and yet of earth, would share our misfortunes with us; He would die like us; He would be buried like us; but, on the third day, He would rise again, and men would see Him resplendent with glory and immortality. What a joy for us, who have within us ‘the answer of death,’ to see such a victory gained by One, who is one of ourselves, ‘flesh of our flesh!’

Thus were the divine intentions to be realized in our regard. Our earth presents to our Creator a new Adam. He cannot stay here, for He has conquered death; He must ascend to heaven, and if her gates be closed, she must open them and receive Him. ‘Lift up your gates, O ye princes! and be ye lifted up, O eternal gates! and the King of glory shall enter in!'[2] Oh that He would take us thither with Him, for He is our brother, and He assures us that His ‘delight is to be with the children of men’![3] But what a joy it is for us to see our Jesus ascend to heaven! He is the holiest, the purest, the loveliest, of our race; He is the Son of a spotless Mother: let Him go and represent us in the kingdom of our inheritance. It is our own earth that sends Him; she is no longer a desert, now that she has produced such a flower, and such a fruit, for heaven. A flood of light poured into this lowly vale of tears, when the gates of heaven were raised up to receive Him. ‘Be Thou exalted, O Lord, in Thine own strength! and we, who are still on the earth, will sing and praise Thy power ’![4] Receive, O eternal Father, the brother whom we send to Thee; sinners though we are, this brother of ours is infinitely holy and perfect. Where is the curse that once fastened on our earth?’The earth hath given her fruit’![5] And if we may presume so far as to see in Him the first-fruits of a future harvest to be gathered into Thy house, may we not rejoice in the thought that the Ascension of our Jesus was the day whereon Thy primal work was restored to Thee?

Let us, to-day, borrow from the Armenian Church one of her sweetest hymns. Let us unite with her in sharing in the joy felt by the holy angels, when they saw the God-Man rising from earth, and taking possession of the highest throne in heaven.

Potestates cœli territæ sunt, videntes ascensum tuum, Christe: alter ad alterum pavescentes dicebant: quis est iste rex gloriæ?

Hic est incarnatus Deus Verbum, qui in cruce peccatum occidit, et supervolans gloriose, venit in cœlum, Dominus fortis virtute sua.

Hic est qui de monumento surrexit, et destruxit infernum, atque superseandens gloriose venit ad Patrem, Dominus potens in praelio.

Qui ascendit hodie divina potestate in patrio curru, ministrantibus ei angelicis choris, qui canebant dicentes: Attollite portas, principes, vestras, et introibit rex gloriae.

Stupuerunt supernae Potestates, et tremenda voce clamabant ad invicem: Quis est iste rex gloriae, qui venit in carne et mira virtute? Attollite, attollite portas, principes, vestras, et introibit rex gloriae.

Modulabantur superni Principatus, mirabili voce cantabant canticum novum, dicentes: Ipse est rex gloriae, salvator mundi et liberator generis humani; attollite portas, principes, vestras, et introibit rex gloriæ.

Qui complantati facti sumus similitudinis mortis tuæ, Fili Dei, dignos fac nos conformes fieri tibi, gloriæ rex; tibi cantent Ecclesiæ sanctorum cantica spiritualia.

Veterem hominem concrucifixum tibi fecisti et stimulum peccati extinxisti; liberasti nos vivifico ligno, cui affixus es, et guttæ sanguinis tui inebriarunt orbem; tibi cantent Ecclesiæ sanctorum cantica spiritualia.

Propter miserationem divinae humamtionis tuæ participes fecisti nos corporis tui et sanguinis, per sacrificium tuum Patri in odorem suavitatis oblatum, corporis a nobis sumpti, et ascendisti pellucidis nubibus, manifestatus Potestatibus ac Principatibus, qui stupefacti interrogabant: Quis est iste qui properans venit de Edom? Et per Ecclesiam tuam didicerunt multiformem sapientiam tuam; tibi cantent Ecclesiae sanctorum cantica spiritualia.

The Powers of heaven trembled, when they witnessed thine Ascension, O Christ, and said to each other in fear, 'Who is this king of glory?'

This is God the Word made Flesh, who put sin to death upon the cross, and ascending in glory, entered heaven: the Lord, mighty in his power.

This is he that rose from the tomb, and destroyed death, and now comes by a glorious Ascension, to the Father: he is the Lord, mighty in war.

This is he that ascended today, by his divine power, in his Father’s chariot: choirs of angels ministered to him, and sang, saying: ‘Lift up your gates, O ye princes, and the King of glory shall enter in!’

The heavenly powers were amazed, and cried unto each other with tremulous voice: ‘Who is this king of glory, that cometh in the flesh and in wondrous power? Lift up, lift up your gates, O ye princes, and the King of glory shall enter in!’

The Principalities of heaven were heard singing a new canticle, and saying in a tone of glad admiration: ‘It is the King of glory, the Saviour and deliverer of mankind! Lift up your gates, O ye princes, and the King of glory shall enter in!

We have been planted together in the likeness of thy death, O Son of God! Make us worthy to be made like unto thee, O King of glory! Let the Churches of the saints sing to thee their spiritual canticles!

Thou didst crucify together with thyself the old man, and thou tookest away the sting of sin; thou gavest us liberty, by the life-giving tree to which thou wast fastened, and thy Blood has inebriated the whole earth. Let the Churches of the saints sing to thee their spiritual canticles.

Through the mercy that led thy divine nature to assume ours, thou hast made us partakers of thy Body and Blood, by the sacrifice of the Body thou hadst taken to thyself, a sacrifice which thou offeredst to the Father in an odour of sweetness. Then didst thou ascend, on a bright cloud, and wast seen by the Powers and Principalities, who asked each other in wonderment: 'Who is this that cometh, in haste, from Edom?’ The faithful have been taught thy manifold wisdom. Let the Churches of the saints sing to thee their spiritual canticles!

[1] Gal. iv. 4.
[2] Ps. xxiii. 7.
[3] Prov. viii. 31.
[4] Ps. xx. 14.
[5] Ibid lxvi 7.