In many traditions the harp is a heavenly instrument, read as peace, grace and spiritual harmony. Its gentle sound in a dream often points to a calm after inner turbulence.
Has this come up in your dreams before? What was going on in your life then?
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.