The Protestant Reformation ocurred in the 16th century. At that time, Europe was undergoing many changes. Below, some of them:
Luther challenged papal authority, and questioned the ability of the Church to define Christian's practices. He, and others ( Calvin and Herny VIII included) wanted power to be distributed evenly. They wanted to purify the Church.
Luther began by criticising the sale of indulgences, insisting that the Pope had no authority over purgatory and that the Catholic doctrine of the merits of the saints had no foundation in the Bible. The Reformation incorporated changes such as the Scriptures as the only source of proper belief and the belief that faith in Jesus, and not good works, is the only way to obtain God's pardon for sin.