The first public reactions to Lutheran teaching in Sweden took place in Stockholm, where Olaus Magnus combated the abominable heresy introduced by German merchants, and in the diocese of Linköping, where Knechts sent by Lübeck for the liberation of Sweden spread the word among Swedish commanders and their men. Bishop Brask issued an open letter in 1522, prohibiting the buying, selling, receiving, or reading of Lutheran works.

A more dangerous strain of the pestilence had already established itself among some of the clergy in the diocese of Strängnäs, where a young cleric just home from Wittenberg, Olaus Petri, or Master Oluf as he became known, served as Bishop Matthias's chancellor. It is not clear how well the bishop understood his protégé; the times did not favor theological discussion. Master Oluf acted as Bishop Matthias's pointman during negotiations in the turbulent spring and summer of 1520, and he was probably present in Stockholm that November, when Bishop Mats lost his head.

After the bloodbath Master Oluf returned to Strängnäs to teach at the cathedral school. His superiors found plenty of matter for offense. One of them, Dr. Nicolaus, drew up a list of eight “Lutheran” heresies in Oluf's teaching, and refuted them point by point. Others, canons at Uppsala, wrote Bishop Brask about the heresy in Strängnäs. Brask sounded the alarm, with letters to colleagues in Kalmar, Skara, and Vadstena. He was too late, however, to stifle the heresy in its cradle.