O Clavis David

 O clavis David et sceptrum domus Israël; qui áperis, et nemo claudit; claudis, et nemo áperit: veni, et educ vinctum de domo cárceris, sedéntem in ténebris, et umbra mortis.

O Key of David, and Sceptre of the house of Israel that openest, and no man shutteth; and shuttest and no man openeth; come to bring out the prisoners from the prison, and them that sit in darkness, and in the shadow of death! 

The 'O clavis David'  stanza from 'O Come, O Come Emanuel':

Veni clavis Davidica!
Regna reclude coelica,
Fac iter Tutum superum,
Et claude vias Inferum.

Gaude, gaude, Emmanuel
nascetur pro te, Israel.

O come, Thou Key of David, come
And open wide our heav'nly home;
Make safe the way that leads on high,
And close the path to misery.

Rejoice! Rejoice! Emmanuel
Shall come to thee, O Israel.

The following is from the New Liturgical Movement

The medieval use of Augsburg in Germany contains a particularly interesting enrichment of the liturgy on these days. Each O is accompanied by a special chapter, and a special concluding oration, both of which refer back to it; these form a kind of scriptural and euchological commentary on the much older antiphons. Like many medieval uses, that of Augsburg also added other antiphons to the series, which I will note in another post next week; here are the chapters and prayers which go with the seven oldest antiphons, those found in the Roman Breviary. At Augsburg, the Os began on December 13th, and so I have noted them here.

December 16 (20 in the Roman Breviary)

Capitulum Dedi te in foedus populi, in lucem gentium, ut aperires oculos caecorum, et educeres de conclusione vinctos, de domo carceris sedentes in tenebris.	The Chapter I have given thee for a covenant of the people, for a light of the Gentiles: that thou may open the eyes of the blind, and bring forth the prisoners out of prison, and them that sit in darkness out of the prison house. (Isaiah 42, 6-7)
Aña O clavis David, * et sceptrum domus Israël; qui aperis, et nemo claudit; claudis, et nemo aperit: veni, et educ vinctum de domo carceris, sedentem in tenebris, et umbra mortis.	Aña O key of David, * and sceptre of the house of Israel; who openest, and no man shutteth; shuttest, and no man openeth: come thou, and lead forth the prisoner from the prisonhouse, and him that sitteth in darkness, and in the shadow of death.
Oratio Aurem tuam, quaesumus, Domine, precibus nostris accommoda: et mentis nostrae tenebras gratia tuae visita- tionis illustra: Qui vivis.	The Prayer Incline Thy ear, Lord, we be- seech Thee, unto our prayers, and lighten the darkness of our minds by the grace of Thy visitation; Who livest.