The fourth of seven Great “O” Antiphons of the liturgy, that date back to the seventh or eighth century. These antiphons are chanted or recited at Vespers, or Evening Prayer, the Antiphon before the Magnificat. They are also the Alleluia verse at the Mass.
O CLAVIS DAVID KEY OF DAVID O Key of David, Scepter of the House of Israel, controlling at your will the gate of Heaven who opens and no man shuts, who shuts and no man opens
R :Come, and bring forth the captive from his prison, he who sits in darkness and in the shadow of death. Isaiah 22:22. Symbols: key; broken chains