O Key of David, O royal Power of Israel, controlling at your will the gate of heaven: Come, break down the prison walls of death for those who dwell in darkness and the shadow of death; and lead your captive people into freedom.
What solace there is this antiphon.
In the 8th century BC King Hezekiah saw troubled times. Sargon the Assyrian invaded. Sennnacherib invaded. You might know the poem of Byron: “The Assyrian came down like the wolf on the fold, / And his cohorts were gleaming in purple and gold...”. They were saved by the Angel who smote the invaders with the plague and slew 185,000 in the night. Hezekiah instituted a religious renewal, which included the suppression of idolatry and polytheism which had grown up over time. Hezekiah, a descendent of David, is
a foreshadow figure of Christ to come. Hezekiah cleansed the Temple. Hezekiah rose from a dire illness on the third day. Hezekiah gives the “key of David” to his steward Eliakim, all his authority, as an office to be handed on.
In Isaiah 22:22: And I will lay the key of the house of David upon his shoulder: and he shall open, and none shall shut: and he shall shut, and none shall open. Government shall be upon his shoulder.
In Matthew 6:19, when the Lord speaks to Peter near the source of the Jordan, we read: And I will give to thee the keys of the kingdom of heaven. And whatsoever thou shalt bind upon earth, it shall be bound also in heaven: and whatsoever thou shalt loose on earth, it shall be loosed also in heaven.
David's key is again mentioned in Revelation 3:7-8: And to the angel of the church of Philadelphia write: These things saith the Holy One and the true one, he that hath the key of David, he that openeth and no man shutteth, shutteth and no man openeth: I know thy works. Behold, I have given before thee a door opened, which no man can shut: because thou hast a little strength and hast kept my word and hast not denied my name.
Like the Philadelphians in Revelation 3, we must never deny the Lord.
The Lord who came in history, will come again at history's end. To point the way to His return, He gave us a visible point of reference, someone to exercise His own authority to open and to shut, to bind and to loose. He gave us His Church with a Vicar in the person of the Apostle Peter and all of Peter's successors. The key is David's, which means, it is the Lord's. And that means that the one who has the keys, acts with Christ's authority, speaks with Christ's voice when he acts and teaches for the Church.
When the Lord died on His Cross and rose again, He fulfilled the debt incurred in the sin of the whole human race. He ransomed “captive Israel”, the new “Israel”, those who belong to Him in His new covenant. The Lord descended to the place where the faithful dead awaited His coming and set them free. This is often depicted as the “harrowing of hell”. When we are in mortal sin, we are already in an anticipation of hell. Christ can set you free through the sacramental confession of your sins to a priest, who unbinds your sins and forgives them with Christ's own authority.