Music's special power is that it goes straight to the emotions, not mediated by concrete imagery as literature and the visual arts are. Any didactic message in the lyrics or in the program notes is even further from its artistic effect. (What about non-representational painting? someone will ask. A Randian answer I think would be that this is not the way our sense of sight works. It needs images of entities, not sense qualities, as our hearing does not.) On top of this, the power of great art in any medium is that it can sell us, at least temporarily, on its sense of life. I don't really feel about the world the way Aeschylus did, but he's had me convinced when I've read him.