From my friend Toddie Downs, at her most excellent blog, WordHappy (at the end of the post, she states explicitly that she is examining the speech from a writer’s perspective only):
…one of the main purposes of the speech was to respond to the inflammatory comments made by Obama’s pastor, Rev. Jeremiah Wright, Jr…
In [his] response, we see Obama’s immediate but measured response to a political controversy. But the speech transcends the controversy. By juxtaposing the conflicting elements within Rev. Wright and also his own grandmother, Obama exposes and juxtaposes his own loathing of racism against the love and loyalty of family. This side-by-side comparison of conflicting elements becomes a thematic motif of his speech, explicitly stated toward the beginning of his remarks:
I chose to run for the presidency at this moment in history because I believe deeply that we cannot solve the challenges of our time unless we solve them together – unless we perfect our union by understanding that we may have different stories, but we hold common hopes; that we may not look the same and we may not have come from the same place, but we all want to move in the same direction – towards a better future for of children and our grandchildren.
I agree completely with Toddie and have referred to this aspect as making the speech universal. It’s the only way to appeal to those who are open enough to listen, since we know, sadly, that not everyone is.