Well...

For most of this book, Wright has been struggling with complicated race relations. From a young age he fought the prejudice. He refused to conform, to become subservient. He strove for equality, to somehow find a way to fix things in his later years, through his work with the Communist party. Wright got screwed. He basically was shunned by everyone in the party, was never allowed back, and ended up being hung up to dry on his own. I think that his realization at the end of the book is that he is not capable of fixing everything between whites and blacks. He finally realizes that no amount of work, no short story, no speech he could make could ever fix the badly misshapen social structure. Instead he realizes, as he puts it, to build a bridge to the outside. Instead of toiling on his own to fight the system, he decides to simply write and publish and give exposure to the issues at hand.