In 1517, a German monk called Martin Luther wrote a letter containing 95 theses criticising the Church. He rightfully opposed the corruption of the clergy and the selling of indulgences.
However, Luther also mocked and denied many truths and good things, such as life in communion with the saints, the authority of the pope, and the explanations given by the Church to better understand the faith. In the end a schism arose in the Church because of Luther’s radical rebellion.