No outside knowledge of the author or historical framework is needed. The power of the words alone can move people to new levels of thought or change the way a person views the world around them. Lines and quotes from poems are extracted and used in the public because they have a wide spectrum of appeal. For instance, the motto of this educational institution is a paraphrase of a powerful quote taken from Chaucer. They could have no knowledge of Geoffrey Chaucer or his life and still appreciate the power of these words completely removed from context.
Words are man's only tools for expressing thoughts or emotions.
It is truly impossible to relate thoughts or emotions perfectly through the use of words, but sometimes a distorted reflection can be found in the imagery of the language. The value of a historical reading of literature would be senseless if that literature had no artistic value. Likewise, if all literature was just shallow usage of flowery language it would never withstand the test of time. A cheap romance novel might entertain you and relate a good story, but the lack of originality in the plot and the haphazard arrangement of imagery will never earn the author a place in history. One is dependent on the other for literature to be successful.