Parallelism
平行结构

I have a dream that one day this nation will rise up... I have a dream that one day on the red hills of …I have a dream that one day even the state of Mississippi…I have a dream….I have a dream today…I have a dream that one day …I have a dream today…I have dream that one day… -Dr.Martin Luther King --I have a dream
General Function
make the speech effective and  forcefulmakethespeechclearandlogicalmakethespeechmorerhythmical  andemotional