Soweto, South Africa (CNN) -- There are still bullet holes in the stained-glass windows of this church.
They're a reminder, Tommy Zwane says, of the dark days before Nelson Mandela became his country's first democratically elected president.
The Regina Mundi Catholic Church in Soweto was at the heart of the uprising against apartheid -- most famously on June 16, 1976, when young students rebelled against the education system and were fired upon by police.
"Things were difficult for everybody, for black people in this country. We used to run and come to this church to pray to God so that he could come and assist us, because we were in trouble at that time," Zwane said. "There was no understanding between us and the government of South Africa."
On Sunday, people filled the church's pews for a very different reason -- to sing, pray and honor Mandela's legacy days after his death in a home nearby.
Services at churches, synagogues and mosques throughout South Africa honored Mandela.
The national day of remembrance is one of a string of events planned to say farewell to the iconic figure who helped South Africa break the practice of racial segregation and end white minority rule.
A massive memorial service is scheduled for Tuesday in Johannesburg's FNB Stadium, which can hold 94,000 people.
A state funeral will be held December 15 in Mandela's ancestral hometown of Qunu in the Eastern Cape province.
At least 70 heads of state and 10 former heads of state have said they're coming to South Africa this week, government international relations spokesman Clayson Monyela said.
From the United States, officials said, U.S. President Barack Obama and first lady Michelle Obama will be accompanied by President Jimmy Carter, President George W. Bush and President Bill Clinton and their wives. More than two dozen U.S. lawmakers are also scheduled to attend.
South African President Jacob Zuma, who announced Mandela's death Thursday, used the revered leader's well-known clan name Sunday as he asked churchgoers to remember the former president's values.
"When I say we pray for the nation, (it) is that we should pray for us not to forget some of the values that Madiba stood for, that he fought for, that he sacrificed his life for," he said. "He stood for freedom. He fought against those who oppressed others. He wanted everyone to be free."
In a suburb of Pretoria, parishioners said they were grateful for the man who saved them from revenge.
"His presence in our lives meant so much for the Afrikaaner 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.
In Soweto, Kathy and Stewart Allen said they don't normally attend the Regina Mundi church. But they wanted to be there on Sunday.
"We believe that this church embodies all the history, and everything that he stood for," Kathy Allen said.
Once again, Stewart Allen said, Mandela has brought the country together.
CNN's Kim Norgaard and Catherine E. Shoichet contributed to this report from Atlanta.