Leaders from at least 91 countries gathered along with tens of thousands of South African citizens to pay tribute to Nelson Mandela in Johannesburg's FNB stadium. Undeterred by a constant downpour, the crowds, which included four U.S. Presidents, celebrated Mandela's life through speeches, dancing, and music.

In his speech, President Obama expressed gratitude to South Africa. "To the people of South Africa - people of every race and walk of life - the world thanks you for sharing Nelson Mandela with us," the president said. "His struggle was your struggle. His triumph was your triumph. Your dignity and hope found expression in his life, and your freedom, your democracy is his cherished legacy."

President Obama went on, challenging himself and other world leaders. "For the people of South Africa, for those he inspired around the globe - Madiba's passing is rightly a time of mourning, and a time to celebrate his heroic life," he said. "But I believe it should also prompt in each of us a time for self-reflection. With honesty, regardless of our station or circumstance, we must ask: how well have I applied his lessons in my own life?"

It is a question I ask myself - as a man and as a President. We know that like South Africa, the United States had to overcome centuries of racial subjugation. As was true here, it took the sacrifice of countless people - known and unknown - to see the dawn of a new day. Michelle and I are the beneficiaries of that struggle. But in America and South Africa, and countries around the globe, we cannot allow our progress to cloud the fact that our work is not done. The struggles that follow the victory of formal equality and universal franchise may not be as filled with drama and moral clarity as those that came before, but they are no less important. For around the world today, we still see children suffering from hunger, and disease; run-down schools, and few prospects for the future. Around the world today, men and women are still imprisoned for their political beliefs; and are still persecuted for what they look like, or how they worship, or who they love.

We, too, must act on behalf of justice. We, too, must act on behalf of peace. There are too many of us who happily embrace Madiba's legacy of racial reconciliation, but passionately resist even modest reforms that would challenge chronic poverty and growing inequality.

Perhaps inspired by Madiba's example of reconciliation, President Obama greeted and shook the hand of Cuban President Raul Castro, the first such interaction between leaders from the two countries since 2000, when Bill Clinton shook Fidel Castro's hand at the UN.

[There was a video here]

At least one leader, however, faced the scorn of the crowd. Current South African Jacob G. Zuma's appearance was met with widespread boos, to the point that the memorial's producers had to replace video of his speech with a photo of Mandela.

[Image via AP]