'Door' in the Bible

I know your deeds. (Look! I have put in front of you an open door that no one can shut.) I know that you have little strength, but you have obeyed my word and have not denied my name.

Listen! I am standing at the door and knocking! If anyone hears my voice and opens the door I will come into his home and share a meal with him, and he with me.

After these things I looked, and there was a door standing open in heaven! And the first voice I had heard speaking to me like a trumpet said: "Come up here so that I can show you what must happen after these things."