I believe that Dimmesdale stands 'on the very proudest eminence of superiority' because he had done his best sermon and has left the crowd in awe.
He spoke about his own life, and what is right and wrong, and that he is not ashamed and should not be judged for fighting for love. His audience is left speechless and after admitting the entire truth to everyone, Dimmesdale dies in the end.
