To transfer one's hatred.

"It was even possible, at moments, to switch one's hatred this way or that by a voluntary act." (Orwell 15).

This quote is an example of how Big Brother and the Party control the population of Oceania. For these people, many things are outlawed and many energies are repressed. People generally stay in their houses except to go to work; they are constantly watched. They have energy that the Party is repressing; physical energy, sexual energy, and all negative energy towards what the Party views as "good" is naturally repressed. The people need an outlet for this energy; thus, it is not hard for the party to channel it into the things they want it to go into. They focus all of the people's negative energy on Emmanuel Goldstein, the leader of a revolutionary party, and on whichever country Oceania happens to be at war with at the time. This energy is not necessarily placed into these things because the people have real hate for them (or real love for Big Brother) but just because they have a lot of energy that needs to be directed at something. The fact that it is easy for this energy to be redirected shows how insincere it is, and also how easy for the Party to manipulate to their needs.