Content warning Contains some information on the plot and some thoughts about it.
On a surface layer "Scanner Darkly" is about the police state through the eyes of a paranoid junkie. Suspicion mixed up with delusion, true and broken friendship, and heavy drug use. However, further into the book and beneath the surface lies the question of a relationship between the god (if any) and man. Building upon St. Paul's "for now we see through a glass, darkly; but then face to face: now I know in part; but then shall I know even as also I am known." Philip K. Dick seems to ask a question: if we do see the god darkly through the glass, does the god see us the same way? If there's no way to know whether you see only the worst in people, could it help to look into morally (and perhaps visually) inverted mirror? Watching his friends and himself Bob Arctor asks that, and wonders if it is someone's obligation to "at least mark their sad comings and goings" "so they’ll be remembered." The answer to this is certainly not present in the book, but sometimes a good question is much better to have and for that I'd recommend reading "Scanner Darkly".