The preaching of Tauler filled him with religious zeal; M. entered into relations with the “Friends of God,” among whom were Heinrich Suso, Heinrich of Nördlingen, Margaret Ebner, and Venturino of Bergamo. In 1377, having purchased the monastery situated on Grünes Wörth island, he rebuilt it and gave it to the Johannites under the name of Altersheim; he himself lived there.
After his death there were found writings of M. in which, without naming them, he had transcribed passages from Tauler, Suso, Ruysbroeck, and others; M. himself had added only alleged visions, conversion stories, and vivid laments on the wickedness of his time.
As H. Denifle proved, the “Friend of the Oberland” is an invention of M., who composed the work to lend weight to his directives among the Johannites. Mystical theology owes nothing to M., and the high esteem in which he was held by Protestants (e.g., J. W. Preger) until Denifle’s researches is unjustified, since as a layman he condemned the hierarchy. The relations of the “Friend of God” with Italy and his journey to Rome are inventions.