He became a teacher in the University of Wittenberg.
He worried about going to Hell and studied the bible to find a way for sinners to get to heaven. The answer he found was 'Justification by Faith Alone'
Martin Luther's message was ignored by the Archbishop, so he wrote down 95 Theses against the sale of indulgences and nailed them to the door at the Wittenberg Castle. The 95 Theses objected to the idea that money could buy salvation.
Luther burned the Papal Bull which was the Warning to Luther to back down.