A motif is a short musical phrase that repeats or reoccurs inside a composition that usually has some sort of importance to the theme or overall meaning of the piece. It's the smallest unit that still contributes to the theme of a composition.
The purpose of Mandela's speech was not simply to address the nation as their new president and give gratitude to those who put him there but instead to make a statement that South Africa was going to make immense changes and unify to show the world what the nation could truly do in order to become a land of hope. There are a few purposes to this speech, one being to unify the nation of south Africa by bringing the blacks and the whites together. The speech was also used to motivate and inspire the people of South Africa. I know this because I've studied Mandela's life in one of my subjects at school.
The audience for this speech was the people of South Africa. He addresses every one he possibly can to broaden his audience so that every South African hears his message.
"I stand here before you not as a prophet but as a humble servant of you, the people."
Mandela repeats the word negotiations as he wants to encourage and push for more negotiations - a thing that will bring them closer to freedom.