The seventh and last of the Great Antiphons, O Emmanuel, rex et legifer...

O Emmánuel, Rex et légifer noster, exspectátio géntium, et Salvátor eárum: veni ad salvándum nos, Dómine, Deus noster.

O Emmanuel, King of Peace, thou enterest today the city of thy predilection, the city in which thou hast placed thy Temple, Jerusalem. A few years hence, and the same city will give thee thy Cross and thy Sepulchre; nay, the day will come, on which thou wilt set up thy Judgment-seat within sight of her walls. But, today, thou enterest the city of David and Solomon unnoticed and unknown.

It lies on thy road to Bethlehem. Thy Blessed Mother and Joseph, her Spouse, would not lose the opportunity of visiting the Temple, there to offer to the Lord their prayers and adoration. They enter and then, for the first time, is accomplished the prophecy of Aggeus, that great shall be the glory of this last House more than of the first (2); for this second Temple has now standing within it an Ark of the Covenant more precious than was that which Moses built and within this Ark, which is Mary, there is contained the God, whose presence makes her the holiest of sanctuaries. The Lawgiver himself is in this blessed Ark, and not merely, as in that of old, the tablet of stone on which the Law was graven. The visit paid, our living Ark descends the steps of the Temple, and sets out once more for Bethlehem, where other prophecies are to be fulfilled. We adore thee, Emmanuel in this thy journey, and we reverence the fidelity wherewith thou fulfillest all that the prophets have written of thee, for thou wouldst give to thy people the certainty of thy being the Messias, by showing them that all the marks, whereby he was to be known, are to be found in thee. And now, the hour is near; all is ready for thy Birth. Come, then, and save us; come, that thou mayest not only be called our Emmanuel, but our Jesus, that is, He that saves us.

The O Antiphon, O Hierusalem; Dom Prosper includes this here because... it was sometimes sung as the last in the series of the Os? I'm not sure, and he doesn't explain. 

O Hierusalem, civitas Dei summi, leva in circuitu oculos tuos et vide Dominum tuum quia iam veniet solvere te vinculis.

The Anglo-Saxon version of O Emmanuel is happily translated in Dr Parker's presentation at her A Clerk of Oxford site, which she maintains as a wonderful archive for our instruction and enlightenment and delight (she writes at the Patreon site these days, as well as at other places). The entire section of the Advent Lyrics is lines 130-163.

Nu þu sylfa cum,
heofones heahcyning. Bring us hælolif,
werigum witeþeowum, wope forcymenum,
bitrum brynetearum. Is seo bot gelong
eal æt þe anum ...... oferþearfum.
Hæftas hygegeomre hider;
ne læt þe behindan, þonne þu heonan cyrre,
mænigo þus micle, ac þu miltse on us
gecyð cynelice, Crist nergende,
wuldres æþeling, ne læt awyrgde ofer us
onwald agan. Læf us ecne gefean
wuldres þines, þæt þec weorðien,
weoroda wuldorcyning, þa þu geworhtes ær
hondum þinum. þu in heannissum
wunast wideferh mid waldend fæder.

Come now thyself,
high King of heaven! Bring healing life to us,
weary slaves in prison, overcoming by weeping,
bitter briny tears. The cure for our great need
depends on thee, entirely and alone.
Seek out the sorrowful captives here,
do not leave behind so great a multitude
at thy return to the heavens, but show mercy to us
in kingly manner, Saviour Christ,
Prince of Glory; do not let the accursed ones
possess power over us! Leave to us the eternal joy
of thy glory, so that they may honour thee,
glorious King of hosts, whom once thou
fashioned with thy hands. Thou dwellest on high
for ever with the Ruler and Father.

"Just as to a medieval Christian time was sharply divided into 'before' and 'after' Christ's entry into human history (hence the A. D. system of dating, popularised in Anglo-Saxon England by Bede), so the poem is divided into the time of prophecies and the time of their fulfilment, bisected by the moment 'when the Son of God would descend to the desolate'. In the second half of the poem the prophets are given a voice, speaking for all humanity, and figured as fettered prisoners appealing to the king for clemency. The imagery and language is all of kingship and of law, building on the antiphon's 'rex et legifer'...."