By the summer of 1518 the causa Lutheri (“the case of Luther”) had progressed far enough to require that Luther present himself in Rome to be examined on his teachings. After his territorial ruler, the elector Frederick III of Saxony, intervened on his behalf, Luther was summoned instead to the southern German city of Augsburg, where an imperial Diet was in session. 

In the Church’s view the key issues were Luther’s denial that the church is empowered to distribute as indulgences the infinite “treasury of merits” accumulated by Christ on the cross—on this point Luther directly contradicted the papal bull Unigenitus Dei Filius (1343; “Only Begotten Son of God”) of Clement VI—and Luther’s insistence that faith is indispensable for justification.