"Whoever controls the past contols the present." What is the meaning of this phrase?

This phrase pertains to the importance of language in any society.  The party argues that reality is not fixed but can be changed simply by using words to do it. They can say 2 plus 2 equals 5 and make it true, just as they can say a certain person never lived--just eliminate all words written about that person and all evidence disappears. By controlling language, therefore, the party can control the past, make it whatever they want it to be or not be, and in doing this they will control the present as well.  Truth lodges itself in language rather than in a reality external to it.  This is what Winston desperately to refuse to believe, but under torture finally succumbs to the power of language controlling and shaping reality.