And to the angel of the church in Philadelphia write: "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. I know your works. Behold, I have set before you an open door, which no one is able to shut." (Revelation 3:7-8a, ESV)When the Assyrians were threatening the city of Jerusalem about 700 B.C., King Hezekiah, a descendant of David, entrusted the master key of the king's treasuries and armories to Shebna, who used his access for personal gain. Hezekaih stripped Shebna of his authority, and gave it to a better man, Eliakim (Isaiah 22:22). During the Assyrian threat, Eliakim was reliable, opening doors for those who needed it and closing them against those who would plunder the king's resources. However, he apparently could not support the weight of his responsibility after that threat ended (Isaiah 22:25).
Revelation uses that key to symbolize Christ's power to open the treasures of his heavenly kingdom to whom he wishes and close them to whom he wishes. In Revelation, Christ has not delegated that key to anyone who may prove to be unfaithful or unreliable. Instead, the Holy One has the key of David. The True One possesses the key that opens and closes the gates to the city and treasuries of the King. Those Jews who had denied the Messiah/Christ, could not claim entrance into the kingdom merely because they were Jews. The Messiah who held the key of David had closed the door to them, and no one could open it for them. On the other hand, those who had confessed Jesus as the Messiah would find that he had opened the door for them, and no one else could close it.