The full quote is, "Who controls the past controls the future: who controls the present controls the past." I believe that in addressing this question, you have to examine the issue of power. The meaning of this statement is that someone can redefine who they are and, in fact, what a society is by being able to change the perception of how the past is configured. For example, dictatorships are very passionate in the idea of "rewriting history." You can see this in Milan Kundera's excellent book, The Book of Laughter and Forgetting. We can also see this in history. When Communist rule was at its zenith of power, governments were driven to recreating history in a manner that coordinated with the current government's goals. In doing this (controlling the perception of the past), more credibility is given to the current, present day policies. The Khmer Rouge government in Cambodia, after they wrestled power away from European control, declared a "Year Zero" where they made the argument that the past is the present. By controlling the means of reading the past, they were able to fortify their control of the present. This is also seen in the French Revolution. After the French Monarchy was overthrown, they instituted a new view of history where the past was considered immoral and evil, lending greater credibility to the present.
I think you want to focus on the idea that people understand their present and future in how they conceptualize and comprehend the past. If someone in the position of power can change how the past is viewed, they have a greater chance of controlling the present in that they are able to link the two together.