The lyrics are below but the music score is here in pdf form. It is originally a Latin 7 verse poem that dates back to the 8th century. It was used in a call and response fashion during the vespers, or evening, service. The original text created the reverse acrostic “ero cras,” which means “I shall be with you tomorrow,” and is particularly appropriate for the advent season. Enya by the way, does not do the whole tune. I couldn’t find anyone on utube who did unfortunately. Here is the Latin version; being a Classicist, I tend to like this one best.
O come, O come, Immanuel,
and ransom captive Israel
that mourns in lonely exile here
until the Son of God appear.
Rejoice! Rejoice! Immanuel
shall come to you, O Israel.
2 O come, O Wisdom from on high,
who ordered all things mightily;
to us the path of knowledge show
and teach us in its ways to go. Refrain
3 O come, O come, great Lord of might,
who to your tribes on Sinai’s height
in ancient times did give the law
in cloud and majesty and awe. Refrain
4 O come, O Branch of Jesse’s stem,
unto your own and rescue them!
From depths of hell your people save,
and give them victory o’er the grave. Refrain
5 O come, O Key of David, come
and open wide our heavenly home.
Make safe for us the heavenward road
and bar the way to death’s abode. Refrain
6 O come, O Bright and Morning Star,
and bring us comfort from afar!
Dispel the shadows of the night
and turn our darkness into light. Refrain
7 O come, O King of nations, bind
in one the hearts of all mankind.
Bid all our sad divisions cease
and be yourself our King of Peace. Refrain