Toward the end of the Middle Ages, the Catholic Church was rife with corruption. The church was split by the Great Schism (From 1378-1417 there were three simultaneous popes, each claiming to be the true pope: Urban VII, an Italian; Clement VII, a Frenchman; and a third pope elected by the Council of Pisa. For several years there were three popes anathematizing and excommunicating one another.). And, the Inquisition attempted to squash any reform movements or attempts to reign in the lavish lifestyles of the clergy by people who could see through the "do as I say, not as I do" speeches given by the clergy to the parishoners.
The scandals that were rife in the Roman church from 590 to 1517 were numerous. Even though priests, monks, and bishops were required to take vows of chastity, ( Celibacy for clergy became Roman Church law in 1079) many nuns and priests engaged in sexual affairs and produced children as a result of these unions. Two popes, Innocent VIII and Alexander VI, fathered and raised children. The convents and monastaries were dens of corruption.
A system of indulgences was foisted upon the public as a way to keep up the luxurious lifestyles of the pope, bishops and clergy who lived more like princes than humble servants of God. These indulgences were sort of like a "free pass" on salvation or an escape from hell if one did a pilgrimage to a particular shirne, purchases a religious relic such as St. Peter's bones, some straw from Jesus' manger or a piece of the "true cross of Christ". The money was used to furnish lavish apartments for the clergy. With the system of indulgences, a very wicked person could "buy his way out of hell" by paying the priests to say the right prayers for his soul.
Because of the lack of "faith" among the clergy, many of the priests were awarded their positions based on family connections or political pull rather than by merit or faith and their ability to read and interpret scriptures. Many priests were illiterate and uneducated regarding the scriptures. They did what they were told by the bishop and by the pope.