He could just wipe my brain, like they did in Men in Black. I'd forget all the junk I mentally ingested -- the songs and memories that pop up in my head at strange times (like during prayer!), the images embedded in my head, my old ways.
Zap me, Tommy Lee!
But instead His word says, "Be not conformed to the patterns of this world, but be transformed by the renewing of your mind, that you may prove what is that good, acceptable, and perfect will of God." The word "be" indicates there is some action necessary on my part in this transformation. At the very least, I have to allow God to work in my life and through my life, and make my mind accessible for change. The process will be even better if I'm an active participant in the transformation process. This means I have to replace old ways of thinking with new ways of thinking, and I actually need to have a "thought process," not just "collections of thoughts."