The O Antiphon for today, December 20, is O Clavis David (Key of David)
Come, and bring forth the captive from his prison.
O Key of David, and Scepter of the House of Israel, who opens and no man shuts, who shuts and no man opens; Come and bring forth the captive from his prison, he who sits in darkness and in the shadow of death.
O Clavis David, et sceptrum domus Israël, qui aperis, et nemo claudit, claudis, et nemo aperuit: veni, et educ vinctum de domo carceris, sedentem in tenebris, et umbra mortis.
The key is the emblem of authority and power. Christ is the Key of the House of David who opens to us the full meaning of the scriptural prophecies, and reopens for all mankind the gate of Heaven.