'Door' in the Bible

'I know your works (behold, I have put before you an opened door that no one is able to shut) that you have a little strength, and have kept my word, and did not deny my name.

Behold, I stand at the door and knock! If anyone hears my voice and opens the door, indeed I will come in to him and dine with him, and he with me.

After these [things] I looked, and behold, an open door in heaven, and the former voice that I had heard like a trumpet speaking with me was saying, "Come up here and I will show you [the things] which must take place after these [things]."