Final answer:
The narrative purpose of the crystal merchant's story about the five obligations of Muslim law is to emphasize the importance of adhering to religious principles in business transactions.
Step-by-step explanation:
The narrative purpose of the crystal merchant's story about the five obligations of Muslim law is to highlight the importance of adhering to religious principles in business transactions. By telling the story, the crystal merchant emphasizes the ethical standards that should govern business practices according to Muslim law. This narrative serves to emphasize the significance of conducting honest and fair trade, as well as the benefits of upholding religious values in commerce.