Symbolism, Imagery, Allegory
Why is Briony always singing little songs and making up stories? Why is Eldric so into making tiny toys and jewelry out of wire and other found objects? Why is Rose always making collages and talking about colors? Why is it such a big deal that Reverend Larkin gives up singing with his daughters? It's all about more than a few silly songs and crafts—in this book, art and music represent creativity, individuality, and life.
The Dark Muses are the best proof of just how powerful art and music can be. They literally feed off of artists (think parasites who like painters and rock stars) in order to stay alive. We're told:
She feeds only on the energy of truly artistic men, draining away their wits. (8.146)
Ugh, right? By forcing their subjects to create, the Dark Muses are literally sucking the life out of their hosts. Briony expresses just how important art and music are as a life force to these Old Ones when she says about her father and stepmother:
[…] it was reasonable to think he'd dealt her a death blow when he stopped singing and locked away his fiddle. She should have unwound and died. (32.79)
A man's artistic nature is even more important than the man himself, which Briony points out by saying, "She doesn't steal the man himself, as the Devil does. She steals his soul and his wits" (11.11). We think it's safe to say that soul and wits are pretty darn important to who a person is, and art and music represent this depth, personality, and vitality.
Adding to the symbolic power of art and music is that fact that artistic communication is used throughout the book to show the true nature of people and situations. We're talking about Rose's collage about Briony and Rose's birthday, the spirits asking Briony to tell a love story, and Briony's constant remembrance of a song about poisoning someone. These are all hints about truth that is hidden in plain sight, clues to the reality that Dark Muses try so hard to hide.