The original question had to be edited down a bit. I think that Faulkner uses repetition throughout his Nobel Prize speech to emphasize his understanding of universal truths by suggesting that their constant presence in the process of composing work underscores their very being. The opening lines which reference the "agony and sweat of the human spirit" help to begin this process of repetition that is seen in different contexts, with the same emphasis. This idea of what it means to be human is repeated when Faulkner talks about the pressing problem of the day in terms of trying to ascertain "when will I be blown up:"
Because of this, the young man or woman writing today has forgotten the problems of the human heart in conflict with itself which alone can make good writing because only that is worth writing about, worth the agony and the sweat.
The repetition of the "agony and sweat" reference helps to emphasize the idea that the toil and pain of what it means to be human is something that not only is present in all of his works, but an idea that Faulkner sees as a universal and human truth that writing should explore. Such an idea is emphasized through its repetition further in the speech, when Faulkner argues that such a basic truth of the "agony and sweat" in what it means to be human will enable human beings to endure, even if it is a "puny inexhaustible voice," it is one that is still talking. It is here where I think that one can see how Faulkner uses the repetition of the endurance of human beings--their capacity to suffer--and how that enables individuals to find some level of strength that will enable them to eventually triumph. It is here where I think that Faulkner's speech is able to use repetition in order to emphasize his understanding of what he sees as universal truths that the modern writer and thinker must evoke in their work and thinking.