Explain the value to the govt of this: "Who controls the past, controls the future. Who controls the present, controls the past"

"Who controls the past controls the future. Who controls the present controls the past."

This quote directly relates to the purposeful revision of history. A government can easily control its citizenry if it controls what they think. Changing the past gives them a direct hold on the present, and the power to revise enables them to dictate and manipulate the future.