People from the church weren't focusing on spiritual and religious lives. The Popes of the church during the Renaissance patronized the arts, and focused on personal pleasure. For example Pope Alexander VI admitted to having 7 kids. This was against what a Pope should be. Many Popes, like Alexander VI were focusing on personal pleasures more than spiritual duties. Many Priests and Monks were not fit for the job. They were poorly educated and some struggled to read let alone teach those readings. Also, they broke their priestly vows by marrying, gambling, and drinking.
To further the Church Corruption, Simony came into play during the Protestant Reformation. Simony is essentially selling church office or roles, or making a profit off sacred things. Jobs were also just being given to family members, this was called Nepotism. Nepotism is the Protestant Reformation version of the Spoils System. Because all these negative things were going on with the church, pluralism rose. Pluralism is the acceptance of more than one religion. Before the Protestant Reformation, the only religion was to be Catholic, but now, because of pluralism there are many different religions.