A door left open is read as vulnerability and the fear of letting the wrong things in. Tradition also sees it as openness to new people or chances.
When this appeared in your dream, what were you feeling?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.