Which factor contributed to the onset of the Protestant Reformation?

The sale of indulgences by the Catholic Church played a significant role in triggering the Protestant Reformation. During the early 16th century, the Church’s practice of selling indulgences—essentially a way for individuals to pay for the forgiveness of sins or to reduce their time in purgatory—was widely criticized for being morally dubious and exploitative. Figures like Martin Luther publicly condemned this practice, arguing that it undermined the core doctrines of faith, grace, and true repentance. Luther’s famous 95 Theses, which he posted on the church door in Wittenberg in 1517, directly challenged the validity of indulgences and sparked widespread debate and dissent against the Catholic Church’s practices.

The criticism of indulgences resonated with people's concerns about corruption within the Church, leading to broader calls for reform. This environment of discontent allowed for the emergence of Protestant movements, which sought to address not only the issue of indulgences but also other perceived abuses and doctrinal errors within the Catholic Church. Thus, the sale of indulgences served as a catalyst that significantly contributed to the onset of the Reformation.