The way the Greek is put together indicates that the door is open in order to stay open, and Jesus underscores that by adding that no one is able to shut it, ever. This promise, of course, links directly to Jesus’ self-identification as the one who has the key to David and so he alone determines access to David’s kingdom/city.
8 “‘I know your works. Behold, I have set before you an open door, which no one is able to shut. I know that you have but little power, and yet you have kept my word and have not denied my name.