Jesus is pretty intent on making it clear to the church in Philadelphia that he is the Jewish Messiah. As far as he’s concerned, it’s an open and shut case. Obviously. He calls himself the Holy One and the True One. He says that he holds the key of David. I’m not exactly sure what that means, but it’s obvious that all of these are significant claims. He also seems to know who is and is not authentically Jewish, and the local synagogue is definitely not a true Jewish synagogue. In fact, he goes so far as to call it a synagogue of Satan. As the Jewish Messiah, Jesus is able to discern who is and is not a real member of God’s family.
What Jesus opens no one can shut; what Jesus shuts no one can open.
When Jesus tells John to tell the church in Philadelphia that he holds the key of David, I think what he means to say is this: I am the only one who can open the door to the Messianic kingdom. The new reality that awaits the people of God is locked, and only Jesus can take us into this awe-inspiring, wonderful space. He is the one who opens or closes the door to new creation. In the Gospel of John, Jesus refers to himself as the gate, and access into God’s family is only granted through him. Here in Revelation, Jesus puts it in even starker terms: What I open no one can shut; what I shut no one can open. There isn’t another way into the Messianic world. It’s Jesus or nothing.