Martin Luther (November 10, 1483 - February 18, 1546) was a German monk, theologian, university professor, Father of Protestantism, and church reformer whose ideas influenced the Protestant Reformation and changed the course of Western civilization. Luther's theology challenged the authority of the papacy by holding that the Bible is the only infallible source of religious authority and that all baptized Christians under Jesus are a universal priesthood. According to Luther, salvation is a free gift of God, received only by true repentance and faith in Jesus as the Messiah, a faith given by God and unmediated by the church.