Winston, in many ways, is the perfect embodiment of 1984's themes about oppression because when you actually look at the character in question, you are observing someone who's already been worn down by that oppression by the time that the story has begun. While he resents the party and struggles against it, he's never an actual threat to it. In fact, much of his rebellion was orchestrated by O'Brien himself.
The final part of 1984 follows Winston as he is tortured by O'Brien. Here we see him being pushed towards and past his breaking point, and it is here that we also learn the ultimate motivation which drives the party to act as it does: it seeks the complete subjugation of the human spirit. In this, Winston again serves as an embodiment for the book's thematic content because this is precisely what has happened to him by the book's final pages: all resistance has been crushed, and he has been left a shell of himself, broken by the Party.