Who was the German priest who challenged the Catholic Church and started the Reformation?

Answer 1

Martin Luther.

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Catholic Answer

During the Reformation better known as the protestant revolt, the Church was challenged by people like Martin Luther to live up to Her Ideals, and to the leadership of Jesus Christ. She was also challenged by the fact that he and others who followed him did wait around for the response - they left. She is still dealing with this situation.

from A Catholic Dictionary, edited by Donald Attwater, Second edition, revised 1957

The Protestant Reformation: the revolt from the Catholic Church in Western Europe begun and carried to its height in the 16th century. It differed from all previous heretical movements in that it was not concerned with one or a few definite points of doctrine but was directed against the whole complex and system of Christianity as then understood; it gave licence to the human self in the spiritual and religious order. Its principal causes were: the excessive temporal power, wealth and privilege which accrued to the higher clergy, the wicked, worldly and careless lives of many of the clergy, secular and regular, and the decay of philosophy and theology (these resulted partly from the Renaissance) with consequent low standard of spiritual life among the people generally; the weakening of the authority of the Holy See, following the Great Schism, increased by the humanistic corruption of the papal court; the parallel insurgence of secular princes. Its principal motives were: desire for the purity of religion and godliness of life which, from the state of the clergy, precipitated a violent and unreasoning anti-clericalism which degenerated into contempt for all spiritual authority; the national ambitions of secular princes which flourished in the break-up of the Catholic integrity of Europe; an appetite for spoil and, as in England, fear of having to give up looted ecclesiastical wealth; in some, a hatred of the Church and Faith which can be attributed only to the direct working of the Devil. The principal results of the Reformation were: the true reform of the Church "in head and members" effected by the Council of Trent and the revivification of Catholicism so thoroughly achieved that it remains vital to this day (The Counter-reformation); the putting of countless souls, notably in Great Britain, Scandinavia and the German parts of the Empire, in enmity to the Church and consequently outside those means provided by Christ for man to know and attain to God; the disappearance of any "higher unity" holding together the diverse peoples and nations of Europe, the inoculation of men with naturalistic and humanitarian (as opposed to theocentric) philosophy which is now the chiefest enemy of Christianity.