Answer: It forces the reader to think about why King is recommending action over negotiation.
King is using logic and arguments in order to prove his point. He states that negotiation is indeed what is ultimately necessary. However, in order for negotiation to occur, a crisis has to take place in order to convince leaders to do so. This is why nonviolent action is useful. King's use of rhetoric forces the reader to think about the reasons why King recommends action over negotiation.