It means, you can only get to Heaven by first admitting to being a sinner. If you're not a sinner, there's no place for you in Heaven, as you are only kidding yourself into thinking you could be a good person without God--or so I interpret religion, I don't believe any of this
So naturally, it is the one who wishes to do the worst, vile things, who would look best while cast under a holy light.
Okay fine you caught me, I was just inverting your quote