91 world leaders head to South Africa to honor Nelson Mandela NEW: President Obama leaves Washington for South Africa He is one of 91 heads of state going to South Africa to honor Nelson Mandela A state funeral will take place Sunday Mandela aide describes sadness and celebration among friends and relatives in his home (CNN) -- More than 90 heads of state are on their way to South Africa for what is expected to be the largest gathering of world leaders in Africa's history. It's a clear sign of what kind of impact Nelson Mandela left on the world. Mandela, the activist who spent 27 years in prison before becoming his country's first black president, died Thursday at the age of 95. U.S. President Barack Obama left Washington for Johannesburg on Monday morning to attend the memorial service for Mandela, which will take place Tuesday in the city's soccer stadium. The 90,000 seats probably won't be enough to house the many mourners wanting to pay tribute to the great anti-apartheid leader. A state funeral will be held Sunday in Mandela's ancestral hometown of Qunu in the Eastern Cape province. At least 91 heads of state and 10 former heads of state have said they're going to South Africa this week, government international relations spokesman Clayson Monyela said. In addition to Obama, former presidents Jimmy Carter, George W. Bush and Bill Clinton will attend. Other guests include the Prince of Wales, British Prime Minister David Cameron and U.N. Secretary-General Ban Ki-moon, as well as celebrities such as Bono, Oprah Winfrey and Naomi Campbell. On Monday, South Africa's Parliament reconvened for an afternoon of speeches and memorials to Mandela. Dozens of members of parliament spoke. "The world over, his name has evolved into a metaphor," Deputy President Kgalema Motlanthe said. The name Nelson Mandela has entered the pantheon of history's sages. Out of the public eye, friends who had not seen each other in years have been coming together with Mandela's family in his home, said Zelda la Grange, Mandela's longtime personal assistant. Mandela called la Grange his "rock," even though she seemed an unlikely confidante. She was a white Afrikaner and an employee of the former apartheid government. In her first interview since Mandela's death, she described the mood in his home to CNN's Robyn Curnow on Monday. "Obviously there's sadness in the house," she said, but also, "People are celebrating Madiba's life. They are grateful. She referred to Mandela by his well-known clan name. South African President Jacob Zuma, who announced Mandela's death Thursday, asked churchgoers on Sunday to remember the former president's values. "His presence in our lives meant so much for the Afrikaner people, allowed them to get rid of their guilt feelings and to participate in the journey that he invited us to join," Wilhelm Jordaan said. Once again, Mandela has brought the country together. READ: Nelson Mandela's death sparks global response READ: Prayers, songs for Nelson Mandela at services in South Africa CNN's Chris Cuomo, Kim Norgaard, Robin Curnow, Arwa Damon and David McKenzie contributed to this report.