Everything of importance seemed to take place in church during medieval times, things like marriage or baptism or funerals. The church was the center of life in a medieval village and each church wanted to be unique and important. Thus we get Holy Relics.
To make each cathedral and each little church in the land unique, each had to have its own holy relic. A holy relic was something that had once belonged to or been touched by Jesus or one of the important Saints. The holy relic might be a bone fragment, a nail from the cross or even a piece of wood from the cross of Jesus.
To churches and especially cathedrals, it was critical to have a holy relic to guard and treasure. One of history's great scholars, Erasmus, once remarked that there were so many pieces of the cross held in churches that you could build a ship.
While most relics were probably fake, people believed holy relics could work miracles. Larger churches might have several relics and the churches traded them and bought and sold them.
In the Middle Ages, all relics, fake or real, had a story. The stories were believed.