Poems of Freedom by John Mulgan
From Introduction:
Great claims have been made for poets as a social force: they have been called the critics of life, the trumpets that sing men to battle, the unacknowledged legislators of the world. On the other hand they have been accused of being introverted neurotics who find in infantile word-play an escape from the serious duties of adult life, the irresponsible fiddlers deserting a Rome in flames. 
Both opinions are bosh, but the second is the inevitable reaction from the first. Those who go to poetry expecting to find a complete guide to religion, or morals, or political action, will very soon be disillusioned and condemn poets, though what they are really condemning is their own attitude towards poetry.
 
Because the medium of poetry is language, the medium in which all social activities are conducted, demands are made on it which it would never occur to people to make on the other arts like painting or music (although, in fact, music is probably a far more effective stimulus to action).
Poets are rarely and only incidentally priests or philosophers or party agitators………
With an introduction by W H Auden.