Washington (CNN) -- As the Martin Luther King Jr. National Memorial was officially dedicated Sunday, speakers called for carrying on King's ideals and values and confronting issues including bullying and social and economic justice for all Americans.





"Nearly 50 years after the March on Washington, our work -- Dr. King's work -- is not yet complete," President Barack Obama said at the dedication ceremony.





The nation faces many challenges, he said, including an ailing economy, substandard education, war and tragedy.





Progress, he said, can often be a slow and painful process. During the civil rights movement, "progress was purchased through enduring the smack of billy clubs and the blast of fire hoses. It was bought with days in jail cells and nights of bomb threats." Every victory was met with setbacks and defeat, Obama said. Today's America can draw strength from that struggle, from King's belief that we are one people and from his refusal to give up, the president said.





"Let us not be trapped by what is," Obama said. "We can't be discouraged by what is. We've got to keep pushing for what ought to be."





He noted that King "will stand for all time, among monuments to those who fathered this nation and those who defended it. A black preacher, no official rank or title, somehow gave voice to our deepest dreams and our most lasting ideas."





"I know we will overcome," the president said. "I know there are better days ahead. I know this because of the man towering over us."





The monument to the slain civil rights leader was due to have been dedicated on August 28, the anniversary of the 1963 March on Washington when King delivered his world-altering "I Have a Dream" speech, but Hurricane Irene forced the event to be postponed.





Perhaps, said the Rev. Bernice King, one of King's daughters, that postponement was due to divine intervention. "Perhaps God wanted us to move beyond the dream into action," she said.





"As we dedicate this monument, I can hear my father saying that oppressed people cannot remain oppressed forever," she said. "The yearning for freedom eventually manifests itself ... I hear my father saying what we are seeing now, all across the streets of America and the world, is a freedom explosion."





She called for "a radical revolution of values and reordering of priorities in this nation."





She urged attendees to also pay homage to her mother, Coretta Scott King, who even as a grieving widow with four children "raised a nation in my father's teachings and values. It was vitally important to her that his life and principles become institutionalized."





The memorial site, which features a striking 30-foot statue of King gazing out on the iconic Tidal Basin, lies between the Lincoln Memorial and the Thomas Jefferson Memorial on the National Mall. The statue, representing a "Stone of Hope," sits forward from a "Mountain of Despair."





Visitors pass through the mountain on their way to King's statue and an expanse along the basin rimmed with an inscription wall covered with stone carvings of some of his most famous quotes. The four-acre area will also feature the iconic cherry blossom trees that draw thousands of tourists to the Mall each spring.





"The very first time that I came to the site, I was almost overwhelmed," Martin Luther King III said. "I really was impressed by this artist. He was able to capture the essence of my dad."





On Sunday, he described his father as "a champion of human rights and social justice for all people," regardless of race, gender and ethnicity.





"Let us not forget that he paid the ultimate price for our civil rights," he said.





But, he said, "we've lost our souls," noting the recent killing of a black man in Mississippi; child bullying; wars in Iraq and Afghanistan; and the lack of social and economic justice
Who said we've got to keep pushing for what ought to be? What did kings children urge? What do the speakers at the ceremony urge? What did speakers at the ceremony urge?
Obama attendees to also pay homage to her mother, Coretta Scott carrying on King's ideals and values and confronting issues including bullying and social and economic justice for carrying on King's ideals and values and confronting issues including bullying and social and economic justice for all Americans.
question: Who said we've got to keep pushing for what ought to be?, answer: Obama | question: What did kings children urge?, answer: attendees to also pay homage to her mother, Coretta Scott | question: What do the speakers at the ceremony urge?, answer: carrying on King's ideals and values and confronting issues including bullying and social and economic justice | question: What did speakers at the ceremony urge?, answer: for carrying on King's ideals and values and confronting issues including bullying and social and economic justice for all Americans.