What does when the music speaks mean?

Music and Literature have always maintained close relations, creating mutual expressive and linguistic solicitations.
Poetry, theater, but also (mostly between XIX and XX century) fiction got interested by the dialectic created by music and literature. At the origins of poetry there's an essential sound element, melodious to the point that it's impossible to just read a poetic song. We need to listen to it, as the ancient authors did with epics.

Essentially, literature and music have the same purpose: recount.
A personal experience or an imaginary story? It doesn't matter, 'cause everything can be used as inspiration for a song or a book.
On the other hand, they are both art forms so they are the mirror of the human soul, the reflection of dreams and feelings.
There's always been a relationship of mutual influence and inspiration between literature and music. However writing a song is not like writing a book. Anyway getting inspired by a great novel to create a song can be a good start point and an exciting challenge. Besides musicians and artists remain fascinated by a book like everyone else and, like everyone else, they can fall in love with a literacy character, reflecting themselves in them so that they can escape from the monotony and the concerns of ordinary life.

The history of music is plenty of tracks which were born this way. For example For Whom The Bell Tolls by Metallica takes its name from the homonym book of Ernest Hemingway: a really suitable work from whom getting inspired to talk about the futility and absurdity of every war.
The band led by Robert Smith, The Cure, got inspired by the novelette of one of the most famous exponent of literary existentialism: The Stranger of Albert Camus. The song Killing an Arab (which led the band to be unfairly accused of racism) is the description of a specific moment of the novel explained by the apathetic protagonist, Meursault.
Anoter example could be David Bowie's album Diamond Dogs which got inspired by 1984 of George Orwell, a distressing scenario of a totalitarian dystopia.

Therefore, quoting the German poet Heinrich Heine:

" Where words leave off, music begins. "