Final answer:
Martin Luther's Ninety-five Theses opposed the sale of indulgences and challenged the Pope's authority, leading to the Protestant Reformation.
Step-by-step explanation:
The publication of Martin Luther's Ninety-five Theses primarily stated his opposition to the sale of indulgences within the Catholic Church. Indulgences were sold as a means to reduce the amount of punishment one had to undergo for sins, essentially offering a "time off" for souls in purgatory. Luther argued that only God could grant forgiveness and that no human, including the Pope, could ensure salvation. The doctrine of justification by faith, as argued by Luther, suggested that faith alone was the key to salvation, not the purchasing of indulgences or any other human action.
This opposition to church practices sparked a debate that would lead to a major shift in the religious landscape of Europe, known as the Protestant Reformation. Luther's theses challenged the authority of the Pope, particularly with respect to pardoning sin and purgatory. His actions eventually led to his excommunication and the establishment of Protestant churches that opposed the Catholic tradition of indulgences.