King: A Life by Jonathan Eig:
On this night, King found a new voice. He discovered or sensed that his purpose was not to instruct or educate; his purpose was to prophesize. With a booming voice and strident words, he marked the path for himself and for a movement. He reminded the people that their advantage was in their moral superiority. They would not burn crosses or pull white people from their homes. They would protest peacefully, as their Christian faith instructed. They meant to reform American democracy, not overthrow it.