The degeneration of the Democratic nomination campaign into identity politics has had (to borrow a term from civil rights law) a "disparate impact" on the candidates. It's helped Hillary Clinton and hurt Obama.
This isn't about taking sides, Obama said. (By noting his mixed parentage, Obama pointed out that he couldn't take sides even if he wanted to without denying a part of himself.)
It's about rejecting identity politics while honoring the nobler aspirations of the identity politicians. And it's about feeling confident that positive social change can be achieved, because it's been achieved in this country in the past. That Obama managed to say all this without displaying an ounce of false piety, or bitterness, or sentimentality, or denial, or self-righteousness, makes his speech a milestone in American political rhetoric.