By “the kingdom of heaven” is meant the Scriptures, because in them the kingdom of heaven is lodged; the understanding of these is the door.
Or “the kingdom of heaven” is the blessedness of heaven, and the door thereof Christ, by Whom men enter in. The door-keepers are the Priests, to whom is committed the word of teaching or interpreting Scripture, by which the door of truth is opened to men. The opening of this door is right interpretation. And observe that He said not, “Woe unto you,” for ye open, but, “for ye shut up;” the Scriptures then are not shut up, though they are obscure.
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).