The face of Nelson Mandela is shown on a large billboard in the stands at the memorial service for former South African President Nelson Mandela at the FNB Stadium in the Johannesburg, South Africa township of Soweto, on Tuesday. – AP SOWETO, South Africa – “Viva Tata Madiba, Viva!” they shouted as the train door opened disgorging hundreds of mourners onto the platform. From the station they walked, jogged, sang and chanted through an unusually rain-sodden Johannesburg morning toward the Soweto stadium, determined to pay their respects to Tata (Father) Nelson Mandela. Bin-bag ponchos and a sliver of the same unwavering determination that vanquished white rule were all they needed to take this, another step along this reborn country's long walk to freedom. “If he was able to stay behind bars for 27 years for us, what is one day, just one rain-drenched day?” asked Musa Mbele. This was an important day for South Africa. US President Barack Obama implored thousands gathered in a cold, rainy stadium and millions watching around the world to carry forward Nelson Mandela's mission of erasing injustice and inequality. In a speech that received thunderous applause at FNB stadium and a standing ovation, Obama said: “We, too, must act on behalf of justice. We, too, must act on behalf of peace,” said Obama, who like Mandela became the first black president of his country. Obama said that when he was a student, Mandela “woke me up to my responsibilities — to others, and to myself — and set me on an improbable journey that finds me here today.” Among the nearly 100 heads of state and government were some from countries like Cuba that don't hold fully democratic elections. On the way to the podium, Obama shook hands with Cuban President Raul Castro, underscoring a recent warming of relations between Cuba and the US. In contrast to the wild applause given to Obama, South African President Jacob Zuma was booed. Many South Africans are unhappy with Zuma because of state corruption scandals. The mood was celebratory. A dazzling mix of royalty, statesmen and celebrities was in attendance.