O Key of David

The fourth antiphon is: "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."
It is the Messiah's prerogative to open or shut the gate into the kingdom. No one else can do this. We call out to him. Come, rescue us for we dwell in darkness and the shadow of death and need to be led into freedom.