What angered Martin Luther about the Catholic Church and how did he respond?

Luther became increasingly angry about the clergy selling 'indulgences' - promised remission from punishments for sin, either for someone still living or for one who had died and was believed to be in purgatory. On 31 October 1517, he published his '95 Theses', attacking papal abuses and the sale of indulgences.

Luther had come to believe that Christians are saved through faith and not through their own efforts. This turned him against many of the major teachings of the Catholic Church. In 1519 -1520, he wrote a series of pamphlets developing his ideas - 'On Christian Liberty', 'On the Freedom of a Christian Man', 'To the Christian Nobility' and 'On the Babylonian Captivity of the Church'. Thanks to the printing press, Luther's '95 Theses' and his other writings spread quickly through Europe.