Jahnn served as the provincial of the Franciscan Province of Bohemia from 1650 to 1658, contributing to the renovation of churches and friaries after their devastation during the Thirty Years' War.
[2] For his contribution to the Church and the Habsburg monarchy, Cardinal Ernst Adalbert of Harrach the of archbishop of Prague proposed he be appointed a bishop in one of the dioceses in a territory under non-Catholic control.
During that time, the Venetians and the Ottomans were fighting the Cretan War, which devastated the diocese, while its population fled to the nearby mountains or Dalmatia.
[7] Jahnn received information on the status of his diocese from the expelled Franciscans who brought with them some 3,000 Catholics from the areas of Livno, Duvno, Glamoč, Uskoplje and northern Neretva in 1659.
[6] Learning about the situation, Jahnn went to Senj from where he informed Francesco Barberini, the prefect of the Congregation on 24 July 1659 about the poor condition of his diocese, simultaneously asking him for the instructions.
[7] Ante Škegro also writes that it is possible that the Bosnian Franciscans were also unwilling to have a foreign bishop on the territory of the Ottoman Bosnia and Herzegovina during an ongoing war.
Dominik Mandić writes that Jahnn was indeed ill, as he was unable to move from his home in Bruck an der Mur from December 1662, when he was carried out on a stretcher to be seen by a papal delegate.