Final answer:
Martin Luther's Ninety-five Theses targeted the Catholic Church's sale of indulgences, catalyzing the Protestant Reformation.
Step-by-step explanation:
Martin Luther published his Ninety-five Theses to criticize the Catholic Church primarily for its sale of indulgences. His Theses argued that forgiveness could only be granted by God, not through the purchase of indulgences, which he saw as a corrupt practice. Luther also challenged the authority of the pope over purgatory and disagreed with the notion that the church could allocate the merits of Jesus and the saints to others. His intent was to initiate a discussion leading to reforms within the church. However, his actions sparked the Protestant Reformation, marking a significant turning point in European history and religious practice.