Superstition
Much of the plot of this book revolves around superstition. Whether the various character believe in the jinn or not is almost irrelevant to determining what other wild ideas they'll believe. For example, the guardians each adhere to strict, ritualistic daily routines in order not to anger the gods. They are nearly older than the building itself and seem to have joined themselves to it karmically. Shah is not naturally prone to superstition, but his wife is. They spend many hours arguing over how to handle their mysterious haunting. A great deal of suspense is garnered in this plot line because of characters who are unreliable narrators explaining what they've witnessed. Their propensity for gullibility discredits much of the testimony, leaving Shah confused and anxious, unsure what to believe. Maybe that's all part of the jinn's plan.
Spiritual Energy Linked to Location
Similar to the western idea of demons, the jinn comes out of Islamic tradition. They are believed to be evil spirits who haunt and stir up trouble wherever they go, even to the point of possession. Unlike the western demons, the jinn possess buildings instead of people. Throughout the story, the characters discover that the jinn's powers are specifically linked to Dar Khalifa, as if he were embodied in the building. Scary though that sounds, it leads to a building-wide exorcism, complete with animal sacrifice. Apparently it works because the jinn leaves (or dies?). Similarly, the guardians are sworn to remain at Dar Khalifa. They've vowed to remain caretakers there and thus are the most qualified to comment about the jinn. The guardians possess unique powers due to their extended residence on the property which makes them absolutely invaluable to Shah. It's as if their powers are tied to the physical property of The Caliph's House.
Heritage
When Shah learns of his wife's pregnancy, he is mainly concerned with raising the child to respect his or her cultural heritage. He goes to great lengths to ensure this child will be prepared to understand where their ancestors came from. This is why he moves to Morocco, a place he visited often as a child. His father always loved the place because it reminded him of their home country -- Afghanistan. In an attempt to steep his family in a cultural similar to their original one, Shah moves to Morocco and accepts the trial of freeing the house from its jinn.
