How did Luther's teaching undermine the power of the clergy and traditional forms piety?

Part of the power of the Catholic clergy came from their authority to hear confessions and forgive sins. Martin Luther, a monk teaching at the University of Wittenberg in Saxony, said that he "hated this God who punished sinners", and turned to The Bible which he re-interpreted to say that man's salvation was not by acts of penance and repentance, but by faith alone. He argued that all Christians are priests and attacked the withholding of the Sacrament from the laity.

Protestantism began with limits on the power of its clergy, and the Roman Catholic Church had, to some extent, to follow suit.