O Oriens

O Oriens, splendor lucis aeternae, et sol justitiae: veni, et illumina sedentes in tenebris et umbra mortis.

O Day-spring, Brightness of Light Everlasting, and Sun of Righteousness:
Come and enlighten him that sitteth in darkness and the shadow of death.

This description derives from the Song of Zechariah, or Benedictus, Luke 1:78-79,

Per viscera misericordiae Dei nostri:
In quibus visitavit nos, Oriens ex alto,
Illuminare his qui in tenebris et in umbra mortis sedent . . .

'Through the bowels of compassion of our God,
Through which the Dayspring from on high has visted us,
To illuminate those who sit in darkness and in the shadow of death . . .'

Notice that our antiphons are proceeding in a chronological direction through the Bible; not in the texts quoted, which are from here, there and everywhere, but in the events alluded to: Creation - Exodus - Jesse - David - and now the beginning of the Gospel, John the Baptist.

The symbolism of light is often applied to Christ in the New Testament, but for specifically eternal light we should look to Isaiah 60, which is all about light. The chapter begins,

Surge, illuminare, Ierusalem, quia venit lumen tuum,
Et gloria Domini super te orta est.

'Arise, shine, Jerusalem, for your light has come,
And the glory of the Lord has risen upon you.'

Note orta, 'risen', the past participle of orior, of which Oriens is the present participle. 

At verse 19 of this chapter we find,

Non erit tibi amplius sol ad lucendum per diem,
Nec splendor lunae illuminabit te;
Sed erit tibi Dominus in lucem sempiternam.

'The sun shall be no more thy light by day;
neither for brightness shall the moon give light unto thee:
but the LORD shall be unto thee an everlasting light.'

This is taken up in the Book of Revelation, or Apocalypse:

Et civitas non eget sole, neque luna ut luceant in ea, nam claritas Dei illuminavit eam, et lucerna eius est Agnus. (Rev. 21:23)

'And the city had no need of the sun, neither of the moon, to shine in it; for the glory of God did lighten it, and the Lamb is the light thereof.'

We should also note the Second Letter of St Peter, 1:19,

Et habemus firmiorem propheticum sermonem: cui benefacitis attendentes quasi lucernae lucenti in caliginoso donec dies elucescat, et lucifer oriatur in cordibus vestris.

'We have also a more sure word of prophecy; whereto ye do well that ye take heed, as unto a light that shineth in a dark place, until the day dawn, and the day star arise in your hearts.'

The 'Sun of Righteousness' comes from Malachi 4:2,

'Et orietur vobis timentibus nomen meum Sol iustitiae, et sanitas in pennis eius.' [note again the use of orior]

'And there shall rise upon you who fear my name the Sun of Righteousness,with healing in his wings.'

To quote a much later writer, Charles Wesley, who continued this highly creative tradition of turning the scriptures into liturgy:

"Christ, whose glory fills the skies,
Christ, the true, the only Light,
Sun of Righteousness, arise,
Triumph o'er the shades of night;
Dayspring from on high, be near;
Daystar, in my heart appear."

Or again, by the same author - quoting it in his original form; we are more familiar with it in the slightly altered form it received from G. Whitefield, M. Madan and others:

"Hail the heavenly Prince of peace!
Hail the Sun of righteousness!
Light and life to all he brings,
Risen with healing in his wings."