It is, in short, about what they hope he will be able to accomplish by following the path he has set out for himself. He also felt it was meant (to a lesser extent) as a rebuke of Bush, Cheney and the neocons, which is one reason why so many Republican heads are exploding over this. The Peace Prize is always political, but this time more so than most. He also felt that Obama's speech was pitch perfect, and that Obama got it right in saying the award was "a means to give momentum to a set of causes" and a "call to action."
See my own thoughts about what this is about here.