'Door' in the Bible

‘I know your deeds. See, I have set before you an open door which no one is able to shut, for you have a little power, and have kept My word, and have not renounced or denied My name.

Behold, I stand at the door [of the church] and continually knock. If anyone hears My voice and opens the door, I will come in and eat with him (restore him), and he with Me.

After this I looked, and behold, a door standing open in heaven! And the first voice which I had heard, like the sound of a [war] trumpet speaking with me, said, “Come up here, and I will show you what must take place after these things.”