Ostensibly, "The Red Moon of Meru" centers around an ordinary theft crime: the loss of a valuable ruby. But the story then examines layer upon layer of theft. The ruby's thief is obscured because the mystic wants to steal credit for the ability to mentally transport substances. (The Master of the Mountain seems likely to me to have been able to deceive himself into thinking that perhaps he had
managed to transport the stone across space and time.)
Taking everything back a step further, the owners of the stone are themselves at least the receivers of stolen goods--heirs to an abbey long ago stolen from the church; and their eastern novelties seem to be at least in part stolen from their original sites. The story even suggests their religious and philosophical beliefs to be a kind of theft; taking what they like from each religion, an abbey here, the eye of a god there, without bothering to devote themselves to the truth of any one of them.
So which theft is the worst? The human law only punishes the theft of a little stone; stealing credit is beyond its scope and it has often been complicit in the great thefts. From a social standpoint, stealing credit or taking advantage of legal thefts are quite acceptable. But only the jewel thief seems to recognize the reality of his sin and thus have a chance at being made right with divine law.