good harmony anticipates the melody, at times encouraging it, at times resisting it, but always anticipating it.
like harmony, the purpose of rhyme, meter, pattern and other poetic elements in verse is to anticipate the meaning.
harmony should never follow the melody blindly. in this way, it is like a marriage relationship. the melody should love the harmony, and the harmony should submit to the melody.
what separates poetry from prose is the explicit form. we use rhyme, alliteration, repetition and patterns to focus and add potency and meaning to the words. often this lets us be more concise, relying on the form to fill in the blanks.