Recurrence means for something to happen over and over again. It is often used for emphasis. In speeches, it is helpful to repeat specific phrases so they get stuck in the mind of the audience. MLK Jr's speech uses repetition with "I have a dream".
Allusion is a reference to another literary work. The most often text alluded to is the Bible. Rhythm is the sound of the words or the meter. Opinion is not really a rhetorical device.
