Winston is tortured; for what? He knows nothing and actually has done nothing. The only person associated with him is Julia, his girlfriend. All they do is meet and have sex.
It seems evident O’Brien was looking for a victim and cultivated Winston. Clearly O’Brien set has taken some pleasure in torturing Winston, and beyond his own sadistic joys, it really is for nothing.
The first time one reads Nineteen Eighty Four, these facts might not be grasped. The second time one can only assume that Members of the Inner Party, like O’Brien, get pleasure from torturing.
As the state is based on Hate it seems clear that those ‘in charge’ are sadists who, with no other outlets, use torture and the demeaning and tricking others as their only joy.
Setting up a meaningless person like Winston Smith is easy, for he is just one of dozens of cogs, simple to destroy and replace.
So much time is taken to make it clear to the reader that Winston Smith is nobody, has never really done anything, and is being tortured to confess to nothing.