The church's corruption.
The church's attempt to raise money by selling indulgences
Answer There were few periods in the long history of the Catholic Church when corruption was more openly present than during the Renaissance period. The sale of indulgences was becoming a prime source of personal income for popes, cardinals and bishops, as were the sale of ecclesiastical offices and the imposition of many corrupt fees and charges.
In 1514, Albrecht of Brandenburg had been raised to the archdiocese of Mainz, but since he intended not to surrender his previous diocese of Magdeburg, and was also under the canonical age to be a bishop, the pope was able to insist on a considerable fee. He agreed in return that 50 per cent of the monies raised from the preaching of the indulgence in Albrecht's two dioceses could be set against this sum. This shoddy deal, made more offensive by the vigour and lack of sophistication with which the indulgence was preached around Magdeburg by the Dominican friar Tetzel, spurred Luther to action.
Also during a visit to Rome, Luther was bothered by the luxurious living, the loose morals, and the lack of interest in spiritual things among the monks they visited. The city, which he had regarded as holy, was a sink of iniquity; its very priests were openly infidel, and scoffed at the services they performed; the papal courtiers were men of the most shameless lives.