Why was martin luther excommunicated from the church

Martin Luther was excommunicated from the Catholic Church by Pope Leo X on 3 Jan. 1521. Martin Luther was a professor at a German University. He wrote 95 theses against the corruption of the Catholic church in charging money for the forgiveness of sins. He used direct and fiery accusations which set the religious catholics against him until he was excommunicated. He was a spearhead figure of Protestantism. Three months later after his excommunication when he was called to defend himself he still stuck by his beliefs.