Obama: "Keep on marching" to fulfill King's dream Aug. 28, 2013: President Barack Obama speaks at the Let Freedom Ring ceremony at the Lincoln Memorial in Washington to commemorate the 50th anniversary of the 1963 March on Washington for Jobs and Freedom.AP President Obama said Wednesday that the iconic words of the Rev. Martin Luther King Jr. "belonged to the ages," as he urged Americans to "keep on marching" to fulfill his dream. The nation's first black president spoke 50 years to the minute after King delivered his iconic "I Have a Dream" speech, in the same spot at the steps of the Lincoln Memorial. Obama offered his personal reflections on the civil rights movement, King's speech, the progress achieved and the challenges that continue to face the nation. Obama spoke often of the "courage" it took for civil rights leaders like King, Medgar Evers, James Chaney, Andrew Goodman and Michael Schwerner to make a difference. "They did not die in vain," Obama told the crowd. Their victory was great, but we would dishonor those heroes as well to suggest that the work of this nation is somehow complete. Obama encouraged Americans of all colors and faiths to "keep on marching." Because they kept marching, America changed. Because they marched the civil rights law was passed. Because they marched, city councils changed and state legislatures changed and Congress changed and yes, eventually the White House changed," Obama said. Obama, as well as former presidents Bill Clinton and Jimmy Carter, were among the headliners in D.C. Wednesday to commemorate the 50th anniversary of the March on Washington. "This march, and that speech, changed America," Clinton declared, remembering the impact on the world and himself as a young man. They opened minds, they melted hearts and they moved millions -- including a 17-year-old boy watching alone in his home in Arkansas. Carter said King's efforts had helped not just black Americans, but "in truth, he helped to free all people." Oprah Winfrey, who also spoke at the ceremony, said King forced the nation "to wake up, look at itself and eventually change." She also said the civil rights leader's lessons inspire people all over the world. Winfrey also said King recognized that Americans shared the same dreams and that their hopes weren't different based on race. She says King was right when he said all Americans' destinies are intertwined and would rise or fall based on how people treat their neighbors. Performers also included Peter Yarrow and Noel Paul Stookey, their voices thinner now than when they performed at the original march as part of the folk trio Peter, Paul and Mary. They sang "Blowin' in the Wind," as the parents of slain black teenager Trayvon Martin joined them on stage and sang along. In his famous speech, King called for the end of racial injustice in the U.S. The march and its effects are credited with helping pass the Civil Rights Act in 1964 and the Voting Rights Act in 1965, both of which insured equal rights for all U.S. citizens.