Part Two - Chapter 10 What does Winston conclude is Goldstein’s final message?
As Winston is caught in his reverie and imagining the woman's life and her singing and her beauty and everything else about her, he thinks that there must literally be thousands and millions of these people all over the world. They are only ignorant of each other because of the lies and hatred sown and perpetuated by big brother but they are all out there and because of this, they are the hope for change.
Winston realizes that Goldstein's final message must be just that, that everything hinged on the proles and their realization of their own place in the world and their power to change it. Without that, all was lost.