At the climax of the March on Washington for Jobs and Freedom, King departed from his prepared text and delivered the extemporaneous 'I Have a Dream' refrain, drawing on biblical cadence and American founding ideals. The speech became the emotional center of the civil rights movement and helped build momentum for the Civil Rights Act of 1964.
King had already delivered versions of the 'dream' imagery in earlier speeches in Detroit and elsewhere, but on this sweltering afternoon in Washington, gospel singer Mahalia Jackson, standing nearby, reportedly called out, 'Tell them about the dream, Martin!' King set aside his prepared remarks on economic justice and improvised, his voice building through repetition until the crowd of a quarter million roared back.
Televised live to tens of millions, the speech reframed the march—originally conceived to press for jobs and economic justice—as a moral appeal to America's founding promises. Its cadences, borrowed from the Hebrew prophets and the Declaration of Independence, gave the civil rights movement a text as enduring as any American political document.
Within a year, Congress passed the Civil Rights Act of 1964, and King himself would receive the Nobel Peace Prize. The speech's closing line, 'Free at last,' borrowed from an old African American spiritual, became etched permanently into the nation's memory of the era.