Gloria Simmons says she took time off work to see the South African leader, who organized a last-minute trip to Montreal on his visit to Canada in 1990.
"Most of all, what I remember is Mandela walking into the church, which was packed, and I was just lucky enough to get a seat right at the back. As he proceeded down the aisle... all I could see was his beaming face smiling," Simmons told All in a Weekend's Sonali Karnick.
Mandela visited the Union United Church in part because it had a committee dedicated to the fight against the apartheid regime in South Africa.
When Mandela learned of the church's contribution in that fight and of its part in promoting his own release from prison, and he agreed to attend a service.
"It was a very proud moment," said Marcus Durant, who was a member of the Union United Church congregation at the time of Mandela's visit.
"He came to Union because we had supported the National African Congress during the dark days and it came to light he had returned to more or less say thank you," said Durant.
Simmons said the most powerful moment of the service was when the choir sang as Mandela and his wife, Winny, walked down the aisle.
"As they sang you could just feel the warmth of the church and the spirit of the people... I was so overwhelmed that I put my hand out to touch him, but the security officer knocked my arm away," she said, laughing.
For Durant, the commemorative service being held Sunday evening at the St. James United Church, should be more of a celebration of his life than a mourning of his death.
"Nelson Mandela brought people together around the world and I think the celebration tonight will hopefully continue to bring people together," he said.
The Commemorative service for Nelson Mandela begins at 7 p.m. on Sunday December 15 at St. James United Church, 463 Ste-Catherine St. W.