It is good that the window should be transparent, because the street or garden beyond it is opaque. How if you saw through the garden too? It is no use trying to 'see through' [everything]. If you see through everything, then everything is transparent. But a wholly transparent world is an invisible world. To 'see through' all things is the same as not to see.
C. S. LewisAll the time the joke is that the word "mine" in its fully possessive sense cannot be uttered by a human being about anything. In the long run either [Satan] or God will say "mine" of each thing that exists, and specially of each man.
C. S. Lewis