How and why was Thoreau important to the study of rhetoric?
Perhaps the most important aspect to Thoreau's rhetoric was his rejection of what he called "long, stingy, slimy sentences," in other words, the verbose writing style of his time. He rather sought to communicate through pithy aphorisms and compact sentences that would stick with the reader:
If the author would acquire literary fame, let him be careful to suggest such thoughts as are simple and obvious, and to express his meaning distinctly and in good language. To do this, he must, in the first place, omit all superfluous ornament, which...tends rather to distract the mind, than to render a passage more clear and striking, or an idea more distinct.
This rhetorical style was in keeping with Thoreau's overarching message of simplicity and even asceticism as the key to morality and happiness. While he had few original ideas, his expression of many Transcendentalist ideas in clear prose makes him an important American writer. While his friend Ralph Waldo Emerson claimed that Thoreau's ideas were "my own, quite originally drest," Thoreau expressed a more down-to-earth, grounded, useful side of Transcendentalist thought, and this was reflected in his rhetoric.
Many Bostonians refused to pay their poll taxes in protest against the Mexican War, and some went to jail. But it was Thoreau who could use rhetoric to demonstrate the potential for this approach, using phrases like "Under a government which imprisons any unjustly, the true place for a just man is also a prison."