Answer:
Grandpa tells his father's story, because he believed that Martin should keep the medicine bag, as an inheritance, in order to give luck and protection.
Step-by-step explanation:
When he is admitted to the hospital and believes that his days of life are ending, grandpa says that it is time for the medicine bag that he carries to be passed on to Martin, since this is an inheritance that is passed on to all the firstborn boys in the family. Martin doesn't want to have that bag, so Grandpa tells the story behind that bag. He says that this bag was given to his father when he was young and was experiencing many difficulties in his village. At that time, Grandpa's father went in search of a spiritual guide and that guide was a piece of iron that he kept in the medicine bag and that protected him, gave him luck and allowed him to survive many adversities.
For Grandpa, the bag is an amulet, a protection left by his father so that all his descendants had a good future and a good life.