Here's an Eric Hoffer quote from his The True Believer:
The true believer] subordinates creative work to the advancement of the movement. Literature, art and science must be propagandistic and they must be "practical." The true-believing writer, artist or scientist does not create to express himself, or to save his soul or to discover the true and the beautiful. His task, as he sees it, is to warn, to advise, to urge, to glorify and to denounce.