First, to say that God is the Judge implies that every act counts, and that what I do is of vital importance, even of cosmic importance. If I believe that God is the judge, and I must stand trial before Him, then I am accountable for my behavior. My life could turn on a single act. If he commits one additional sin, he tilts the scale of guilt against himself and the entire world and causes it's destruction. But if he performs one good deed, he swings himself and the whole world into the scale of merit and causes deliverance.
History is replete with countless examples of small acts that changed the world.
No one lives in a vacuum. What we do, can change the course of history, not to mention our lives. There are no equations here, of course, but to dwell on this image is to tremble before you act. Second, to say that God is judge, means that God must care about what I do. This is a basic human need.