The Ministry of Truth Symbolism
The Ministry of Truth symbolizes the Party’s belief that power is the most important commodity that they have access to. And the power over what people believe (which includes power over the past) is part of that equation. As they change the past, they are ensuring that no one ever comes upon information that contradicts the persona Big Brother has and the concept the citizens have of the strength of their government. The ministry can make truth whatever they want it to be, something that comes back around at the end of the novel when O’Brien is attempting to make Winston see that 2+2=5.