Fox, of course, was a straight down the line Christian who identified the Light with Christ, although some surfing confirms that modern Quakers don't all agree with him. Carter seems to give a more universalist picture of Fox than Fox's writings allow for. Of course, I prefer Carter's version :-)
My former self regarded the idea that the light is in everyone as terribly unsound. Now, of all that I believed, what persists is a recognition of the light in people around me, whether they are Christians or not, and a belief that the light will win, in spite of the darkness which closes around it. Given the state of the world, maybe this belief is just as irrational as any religion, but as long as I continue to find light shining from new places, I will believe it.