Answer:
Thoreau gave much thought to his form of rebellion.
Explanation:
This is the sentence that best expresses the main idea of the paragraph. The sentence tells us that Thoreau had thought about his ideas carefully, and that he had a well-constructed, logical justification for civil disobedience. Thoreau clearly had spent a lot of time thinking about this form of rebellion. He was not only convinced of his position but he summarized his views in his essay.