As he sat in a “narrow jail cell” in the city of Birmingham in 1963 — just five years before his death — Martin Luther King Jr., then imprisoned because he’d violated a court injunction against public civil rights demonstrations, read a newspaper statement questioning his and others’ methods of pushing for civil rights reforms. The statement, authored by eight moderate clergymen, criticized the use of public demonstrations and urged activists to stick to the electoral and legislative processes to bring about the reforms they sought.

The letter grieved King so much he wrote more than 6,900 words in response on any paper he could get his hands on, in the margins of the newspaper and on other bits of paper supplied by a trustee and his lawyers. That “Letter from a Birmingham Jail” explained in forthright terms how King believed nonviolent protest would spur action by those with the authority to change segregationist laws. It went on to become an iconic document of the civil rights movement and is still discussed in schools today, more than 50 years after its composition.

“We know through painful experience that freedom is never voluntarily given by the oppressor; it must be demanded by the oppressed,” King wrote. “For years now I have heard the word ‘Wait!’… This ‘Wait’ has almost always meant ‘Never.’ We must come to see, with one of our distinguished jurists, that ‘justice too long delayed is justice denied.’"

He pointed out that of all the protests he’d participated in, not one had been judged timely in the eyes of people who hadn’t experienced segregation. They always told him, he said, that the passage of time would surely bring better race relations. But he knew that wouldn’t happen by itself.

“Human progress never rolls in on wheels of inevitability,” he wrote; “it comes through the tireless efforts of men willing to be coworkers with God, and without this hard work, time itself becomes an ally of the forces of social stagnation.”

King grounded his belief in nonviolent agitation in what he had read in the Bible and in the history books telling of the nation’s founding. He found inspiration in the disobedience of the Jewish figures Shadrach, Meschach and Abednego and the ancient Christians who chose death rather than adhere to laws contrary to their conscience. He cited the Boston Tea Party as “a massive act of civil disobedience.”

And with the certainty that what he was doing was right, he submitted to his imprisonment, unjust though he believed it to be. He did so because, he said, “an individual who breaks a law that conscience tells him is unjust, and who willingly accepts the penalty of imprisonment in order to arouse the conscience of the community over its injustice, is in reality expressing the highest respect for law.”

In other words, he believed so much in the ideals of justice and lawful order that he was willing to expose how our nation fell short of those ideals.

King may not have known it, but he was a man for his time, uniquely equipped to lead our nation away from its racist practices and toward fulfillment of the promises of “life, liberty and the pursuit of happiness” on which it was founded. His principles of determined nonviolent action remain relevant as we prepare to honor his legacy on Monday.