What is the role of the Brotherhood in 1984?

The Brotherhood is the secret, anti-government organization headed by Emmanuel Goldstein. Whether or not the organization really exists is not made 100% clear, but it is doubtful that it exists. More likely, it, as well as Goldstein, are made up by the government of Oceania as a means of seeking out revolutionaries and anarchists. Also, by letting people believe that this person and organization exists and then by showing people the terrible fate that befalls those who join or associate with this organization, the Party keeps people in line. People see or hear about the tortures carried out against anyone who tries to go against the Party and their fear of that happening to them keeps them from going against the Party. In the story, Winston tries to join the Brotherhood and that is how O'Brien traps Winston and Julia who eventually are tortured into loving Big Brother and the Party. Essentially then, the Brotherhood is merely bait dangled by the Party to catch those who might want to overthrow the government.