Orlando ages, travels, and changes gender. So what makes this a novel about one person? It isn't about just one person: Orlando reflects herself in Chapter 6, there are thousands of selves presented on the written page. People change from moment to moment. But there is a core, to both Orlando and to Orlando. The core is "The Oak Tree" − Orlando's dreams and reflections. It is the inner life of the character that gives Orlando her identity, not the social trappings of her clothing or her body.
Even though Orlando is a novel about shifting identities, Woolf acknowledges that you can't entirely throw off what you're born with. Orlando's changing gender creates restrictions: it changes her sexual desire, and forces her to deal with discrimination that she never encountered as a man.
Orlando’s sex change allows him (or her) to come to a greater understanding of his (or her) essential identity.