I've seen a pattern in a couple of titles.
- Asimov has a book called "Through a Glass, Clearly".
- Philip Dick wrote "A Scanner Darkly".
- Star Trek has the episode "In a Mirror, Darkly"
- Agatha Christy wrote the story "In a Glass, Darkly"
Curiously, 3 of the 4 are sci-fi. Any reason for the commonality of phrasing? Does it have some sort of meaning? Anyone know how it originated? Is it used in spoken English?