I turn on a light in a dark room, and the vermin scatter. The cockroaches won't normally come into the light unless they've run out of darkness to hide in. The rats and mice stay in the walls and attic where it is dark, so that by darkness they will not bee seen, and by not being seen they will remain safe. When I turn on the light, the burglar jumps out of the window into the night, because his deed is exposed, and he feels threatened.
I turn on the light so that I can see plainly what I am doing. My wife comes into the light so that she can also see what I am doing. What am I doing? I'm stomping on cockroaches, of course!
These verses, when taken in context, denote two types of people: those who come into the light, and those who do not. Therefore, everyone cannot fall into one category, or there would be no one left to fall into the other (Turn out the lights and they all fall into something).