Answer:
An indulgence is the total or partial forgiveness of sin given by the Pope and received by God. In the 16th century, indulgences caused the Reformation because they were arbitrarily given and, in some cases, the indulgences were sold. Despite the market of indulgences were not new (since the 13th century this practice was made), it is in the 16th century that it intensifies.
Step-by-step explanation:
The role of the market of indulgences in the Reformation is because this practice leads to corruption. In the 16th century, the Catholic Church was the most influential and rich institution on Earth, but she was concerned only with wealth. The market of indulgences was only a part of this corruption. Martin Luther didn't accept this and fought against the sale of indulgences writing his 95 theses (what he didn't accept or considered right in the Church). The Reformation began when he fixed his theses at the door of the Cathedral of Wittenburg.