"He who controls the present, controls the past. He who controls the past, controls the future."
That quote basically summarises the entire reason for the past's importance in 1984. Given that this is a unit 4 SAC (and thus more interpretative) it could also be useful to contrast that with the age old adage, "history is written by the winners".
Anyway, it'd probably be good to start with a paragraph highlighting the importance of history for the party's purposes. If the party controls the past, then there is no frame of reference which the citizens of Oceania are able to compare their current living standards against. For instance, the Party portrays pre-IngSoc Air Strip One (England) as being a world where the capitalists exploited people ruthlessly. By contolling the past the Party is thus able to portray pre-IngSoc society as being decadent, and take the credit for pre-IngSoc inventions which hence elevates the Party's status in Oceanian society. It is unlikely that the people would protest or attempt to overthrow a regime which they believe is bringing unheralded prosperity to them. If the people had known the real pre-IngSoc world (so, 1940's England) they would have had a society which to compare their own to and thus a reason to be angered by the developments in Oceania.
It'd probably also work well to outline the importance of the Records Department in terms of maintaining party control in Oceania. This be first manifest within the day-to-day editing of information such as the deletion of information relating to people who have been vaporized. If the Party was to allow such information to exist, then people would begin to question the judgment of the Party. For instance, if the Party were to allow for traces of information such as the fact that Oceania used to be at war with Eurasia, not Eastasia to exist, then it would show that the Party can at times be wrong. The Party relies upon its judgment being infallible in order to maintain its stringent control over the population. This is similarly the case when the Party is going to drop the chocolate ration despite a promise not to do so, thus requiring Winston to edit history to remove that promise. If such a promise could be proven to exist, then the Party would certainly run into dismay from the people.
Another more conceptual thing you could look into is the link between controlling history and doublethink and how they are inextricably dependent on each other.
Hope that helps somewhat!