It seems as if a lot of people on this board have addressed the mirror as an opening for the singer to channel the rest of the world/America to change. Although change is, in fact, greatly addressed in the song, I believe looking at himself in the mirror is a type of realization that comes before the act. The singer knows he must change, but it seems sort of obligatory where and how he should change. Here is where the song seems more of a self-realization of who the singer is before he decides where he wants to be (That's Why I'm Starting With Me/I'm Asking Him To Change His Ways). The word “change” here better implies the indication of the beginning. He wants to go out and save the world, but he knows that it is a dream of grandeur to just begin with others. However, if he wants to start on the right path towards helping the world, he must help himself.
Also, relating to Hall, it seems as if the singer is influenced by the environment around him. Towards the end of the song, the singer tells his audience to take a look at themselves in the mirror and make the same change. Although most would read that as instructional, I think it could be read as if the singer is calling for help. In order to make the change himself, he needs to see others doing the same.