Long robes are traditionally read as dignity, ceremony and spiritual or learned authority. They can stand for a calling, or for a role that asks you to be wiser than you feel.
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.