The division of christianity emerged when a catholic monk questioned the selling of indulgences and began preaching

Martin Luther in 1517 in his "Ninety-Five Theses", which he ceremoniously posted on the door of the All Saints' Church in Wittenberg, stood for the justification by the faith alone. His belief that salvation is a free gift of God’s grace that comes trough the faith in the figure that redeemed mankind from sin, Jesus Christ, put Luther at odds with the Pope who advocated the selling of indulgences as way of clearing oneself from sin.