I'm writing a piece about 1984, and I want to rephrase this sentence so that it's more... understandable:
In April of 1984, Oceania is at war with Eurasia; citizens must force themselves to "remember" that they have always been at war with Eurasia, despite the fact that Oceania was allied with Eurasia only four years before. Failure to control their thoughts using doublethink, would result in thoughtcrime.
Your quote from the novel is the central idea of George Orwell's message in 1984. In order to keep the citizens both obedient and reacting out of fear, the government keeps them in a state of war. The point is that it is irrelevant who Oceania is at war with - only that they ARE at war. The proganda spread by Oceania's government focuses all the anger and resentment that the citizens about being controlled and it gives people someone to hate. Someone to blame. It is easier for the citizens to simply believe what they are told, even though it goes against what they know to be true (what country is the "enemy"), so they are all experts at double-think. The main character struggles not to commit thoughtcrime, because he is in charge of changing the history, so he knows the truth about the lies being told by the government. Ultimately, citizens who are more able to simply do what they are told and think what they are told are better off than those who question the government or rebel against the rules. Critical thought is not encouraged; blind obedience is the best way for citizens to exist.