Yama tests a person's capacity to demand. Does he want it first? And does he want it enough to, is he capable, and is he willing to put forth that effort? For the shopkeeper, demand is when you want something and you have the ability to pay for it,. You are willing to buy it, and you go in there and you buy it. Yama: "You must come into a monastery on your own power"
Swami Sarvapriyananda teaches the Katha Upanishad, which is one of the most popular Upanishads. The scripture concerns the story of a young man who goes to the house of death to find out what happens after death. The reply describes the nature of reality and the meaning of life.