What was one reason Martin Luther disagreed with the Catholic Church?

One major reason Martin Luther disagreed with the Catholic Church was his strong opposition to the sale of indulgences. Luther believed that the practice undermined the core principles of Christianity by suggesting that salvation could be purchased rather than being a gift from God received through faith and repentance. The church's marketing of indulgences, which were certificates that purportedly allowed individuals to reduce punishment for sins, seemed to him to distort the true nature of God's grace. This conviction drove him to write his famous Ninety-Five Theses, which criticized the abuses within the church and called for reform, sparking the Protestant Reformation. Luther's stance was foundational in challenging the authority of the church and establishing separate Protestant traditions that emphasized personal faith and the reading of scripture.