A mirror does a great job showing me the dirt on my face, a cheeseburger I shouldn't eat, or a pimple that needs popping. I would be silly to use that mirror to fix any of that or try and wipe my face with it. The law is the same way, it shows me my imperfections, sins, and my needs for cleaning up. That is where Jesus comes in. By faith, I can run to Jesus (Grab a rag) and be cleaned up by His blood and His life within me.