The 'O Antiphons' (an antiphon is a spoken response in a church service) have been used in liturgical Christian traditions since as far back as the sixth century. They are spoken before reading the Magnificat at Evening Prayer during the last seven days of Advent.
My thanks to Malcolm Guite for these poetic reflections. Here is the one for 21st December: O Oriens – O Sunrise
O Oriens, splendor lucis aeternae,
et sol justitiae: veni, et illumina sedentes
in tenebris, et umbra mortis.
The minute dial added in 1759 to a 15th-Century astronomical clock in Exeter Cathedral O Morning Star,
splendour of light eternal and sun of righteousness:
Come and enlighten those who dwell in darkness and the shadow of death.
E vidi lume in forme de riviera Paradiso XXX.61
First light and then first lines along the east
To touch and brush a sheen of light on water
As though behind the sky itself they traced
The shift and shimmer of another river
Flowing unbidden from its hidden source;
The Day-Spring, the eternal Prima Vera.
Blake saw it too. Dante and Beatrice
Are bathing in it now, away upstream. . .
o every trace of light begins a grace
In me, a beckoning. The smallest gleam
Is somehow a beginning and a calling:
“Sleeper awake, the darkness was a dream
For you will see the Dayspring at your waking,
Beyond your long last line the dawn is breaking.”