Final answer:
Henry David Thoreau's excerpt from "Resistance to Civil Government" mainly employs irony as a rhetorical device, criticizing the government's urgent demand for taxes contrasted with the higher value of life.
Step-by-step explanation:
Henry David Thoreau, in the excerpt from "Resistance to Civil Government," primarily uses irony as a rhetorical device. He contrasts the immediate value of life with the comparative insignificance of money to criticize the government's demand for taxes, suggesting that the government’s desperation does not warrant his haste to comply. Thoreau's use of irony here emphasizes his belief that individuals are not responsible for the operating of society's machinery and should resist governmental demands when they are unjust or infringe upon one's individual freedoms.