'Door' in the Bible

I know your works. Because you have limited strength, have kept My word, and have not denied My name, look, I have placed before you an open door that no one is able to close.

Listen! I stand at the door and knock. If anyone hears My voice and opens the door, I will come in to him and have dinner with him, and he with Me.

After this I looked, and there in heaven was an open door. The first voice that I had heard speaking to me like a trumpet said, “Come up here, and I will show you what must take place after this.”