What was known as a Letter of Indulgence?

A Letter of Indulgence was a pardon certificate issued to those, who paid money to the Church, for remitting punishments for their sins both in this life and after their death. It was issued by Pope Leo x, who needed money to build St. Peter's Church. Normally, the priest imposed a penance or punishment on a person who had sinned and he was required to perform a special service or make a pilgrimage to a holy place. But now they could be freed from doing penance for their sins by buying a Letter of Indulgence.