Art is that which rubs people -- gives them an itch or a caress -- in a spot which they forget otherwise existed. A book which demands we remember there is another perspective, a poem which demands we feel some other feeling.
Everyone has a different perspective -- but art isn't merely a different perspective, but also a different perspective which reminds us that we'd forgotten or never met that element of our own perspective.
This can be pleasant or not. And thus, art. That is also why propaganda fails -- who could forget the dominant perspective? Propaganda does not rub an unfelt spot -- it makes certain that there is no rubbing of unfelt spots.