You asked where it states roles for classes. There you go. They are also in the character generation screen, though abbreviated. It does not say they are only healers -- it does make clear what their most common role is.
And for the record, I didn't say one word to this guy who wasn't healing. I treat divines well in-game, whether you want to believe that or not. I brought up the example because of the suggestions that non-healing divines don't exist.