Differences between Catholics and Lutherans during Medieval/Renaissance times?

The most drastic difference would be in treatment of the Catholic Church and the political activities of the Popes during the Middle Ages and Renaissance. Even a devout Catholic would have to admit, as Catholic historians do, the deep corruption of the Church in the Renaissance period, but would probably emphasize the genuine spirituality that existed in many of the Orders within the Church. A Lutheran would be much harsher on quite a few topics: the Crusades against heretics, the political ambitions of the Popes, the immense secular wealth of Church institutions, etc.