Martin Luther King's efforts were inspired by Thoreau's definition of Civil Obedience being his words an extension of Thoreau's in his text. Both of them went to jail under a law that they resisted to, which is a form of peaceful political protest. In the Thoreau's "On the Duty of Civil Disobedience" we get the same message that we get from King's letter:
"Under a government which imprisons any unjustly, the true place for a just man is also a prison."
(...) It is there that the fugitive slave, and the Mexican prisoner on parole, and the Indian come to plead the wrongs of his race, should find them; on that separate, but more free and honorable ground, where the State places those who are not with her but against her,—the only house in a slave-state in which a free man can abide with honor. If any think that their influence would be lost there, and their voices no longer afflict the ear of the State, that they would not be as an enemy within its walls, they do not know by how much truth is stronger than error, nor how much more eloquently and effectively he can combat injustice who has experienced a little in his own person."
The excerpt above it's similar to Luther King's because it shows that even from jail, the one who find a law to be unjust and suffers it's penalty, is able to show society how unjust this law is, this attitude may change the law quicker , as many just men suffers from it.
