What does Isaiah 22:22 mean?

In the modern world, the "key to the city" is sometimes given out as an honorary award by some mayors. This symbolizes the idea that the person has earned such respect that the entire town welcomes them. Such ceremonies usually use an oversized, decorative key which doesn't open any actual lock. Nor does the ceremony truly bestow special rights. Yet here, Isaiah is not referring to an honor in title only. This new leader was given management over crucial aspects of Jerusalem's resources.

The Lord declares His intention to grant authority to Eliakim: the new steward of the king's court. This man of God and father-figure to the nation will wear the key to the house of David. As with the modern ceremony, this may have involved a physical item representing authority. The gates of a city were its most important point of security and commerce. A man with power over those had the authority to decide who will be allowed to have an audience with the king and who will be excluded. The king's decision to give the key to Eliakim, by the Lord's will, is a sign of great respect and trust. The one who carried this responsibility exercised authority in the name of the king. Eliakim was the final word on whether the gates remained open or closed.

The key of David, and the authority that comes to the key-bearer, is mentioned again in Revelation in the context of spiritual doors: "The words of the holy one, the true one, who has the key of David, who opens and no one will shut, who shuts and no one opens" (Revelation 3:7).