On October 31, 2017, people all over the world celebrated the 500th Anniversary of Martin Luther nailing his 95 Theses on a cathedral door in Wittenberg, Germany. Martin Luther was a Catholic monk; as a monk, he came to learn a lot about the Bible. In fact, he was so educated about the Christian faith that he earned a doctorate of Theology in 1512 and soon later became a theology professor at the University of Wittenberg.
In his theses, Luther decried the Pope and the Catholic Church for corruptions that he saw in the Church. He believed that the Catholic Church was abusing its power. One of his primary concerns was with indulgences, which were pardons offered by Church leaders that people could purchase to supposedly erase their sins. The people thought that they could purchase this supposed insurance that could protect them from being punished in Hell. Luther, however, did not see any evidence of this in scripture. He felt that the Catholic Church was gaining money unfairly by assuring people (without scriptural support) that they could buy their way out of their sins. In fact, some people even tried to buy forgiveness for dead relatives. Luther realized that indulgences brought plenty of money to the Catholic Church. He challenged their system of indulgences, believing that it was focused more on money than the forgiveness of people's sins. Many of Luther's 95 Theses focus on the Catholic Church's practice of selling indulgences. For example,
"Therefore those preachers of indulgences are in error, who say that by the pope's indulgences a man is freed from every penalty, and saved."
#21 claims that anyone who preaches that the pope's indulgences can save people from all sins is wrong.
"Christians are to be taught that he who sees a man in need, and passes him by, and gives [his money] for pardons, purchases not the indulgences of the pope, but the indignation of God."
#45 discusses the hypocrisy that Luther saw being taught in the Catholic Church. People thought that they could walk past a poor person without helping them financially. Then, they could pay money for an indulgence and be forgiven for their sins. Luther taught that this was a lie and that spending money on indulgences (rather than helping others) upset God.
In 1521, Martin Luther was excommunicated from the Catholic Church. He ended up teaching people independently and grew his own church, which became known as the Lutheran Church. He was one of several reformation leaders who led to major changes in Christian worship, including leaders such as John Calvin and Jan Hus. These new branches of Christian churches (today known as Protestant churches) eventually led the Catholic leaders to have their own counter-reformation, where the Catholic Church re-evaluated some of their practices. Luther led many people to reconsider what the Bible taught and to seek to purify the practices and teachings in churches.