Let's say you were in a car accident and your car needs both body and engine work. Would you be satisfied with the repair shop slapping some polish on the crumpled fenders and hood? Sure, you may have a shiny car, but the body is still crumpled and the engine is still knocking!
When people ask me to edit their book manuscript, I suspect all they expect me to do is slap some polish on the crumpled fenders and hood. In other words, they want me to proofread their manuscript--while the body is still crumpled and the engine is still knocking!
Body work is hard work. I took an auto body class in college and with wide eyes discovered all the work that goes into it! There's the hard work of straightening the frame, then applying filler, then sanding with a coarse grit, then sanding again, then applying more filler, then sanding with a finer grit, then sanding again and again and again, then applying primer, then applying paint, then applying sealer ... whew! And then the car goes to the mechanic to repair the engine.
But when the car is done, you have a stunning vehicle that not only looks great but drives like a dream as it carries you to your destination.
Editing is far more than polishing a manuscript. It is the hard work of straightening the frame, filling in gaps, sanding down rough places, then sanding again and again, fixing inconsistencies, replacing weak words with stronger words, all while keeping the author's voice. Editing is body work, engine work, and polishing work!
And when the editing is done, you have a stunning manuscript that not only looks great but drives like a dream as it carries you to your literary destination.