The caged bird singswith a joyous songof the captive life that kept it safe all along.This answer exemplifies the two birds: free and caged. Free in such a way that it is able to sing a song of its choice, and caged, because even if it is in captive it has something to be thankful for, its safety.
Henry David Thoreau was an American essayist, poet, philosopher, abolitionist, naturalist, tax resister, development critic, surveyor, and historian, two of his greatest works are: "Resistance to Civil Government" (also known as "Civil Disobedience") and "The Mask of Anarchy". His ideals can be summarized by this statement: “the Government should not have more power than the bestowed by its citizens”.
Henry David Thoreau was even imprisoned for refusing to pay taxes in protest for the Mexican-American War and the slavery.
In this passage from Walden, Thoreau the analogy is:
He is comparing life to a moving train
Here we have the evidence to support the analogy:
Let us spend one day as deliberately as Nature, and not be thrown off the track by every nutshell and mosquito's wing <u>that falls on the rails.</u>
He us trusted with money and bills