Fidelis was still guardian of the community at Feldkirch when in 1621 he was appointed to undertake a mission in the country of the Grisons with the purpose of bringing back that district to the Catholic Faith.
In 1611 he returned to Freiburg to take the doctorate in canon and civil law, and at once began to practise as an advocate.
But the open corruption which found place in the law courts determined him to relinquish that profession and to enter the Church.
Before setting out on this mission Fidelis was appointed by authority of the papal nuncio to reform the Benedictine monastery at Pfafers.
He entered upon his new labours in the true apostolic spirit.
On re-entering the country of the Grisons he was met everywhere with the cry: "Death to the Capuchins !
" On 24 April, being then at Grusch, he made his confession and afterwards celebrated Mass and preached. On the way his companions noticed that he was particularly cheerful.
As a preacher his burning zeal earned for him a great reputation.
From the beginning of his apostolic career he was untiring in his efforts to convert heretics nor did he confine his efforts in this direction to the pulpit, but also used his pen.
Throught the winter Fidelis laboured indefatigably and with such success that the heretic preachers were seriously alarmed and set themselves to inflame the people against him by representing that his mission was political rather than religious and that he was preparing the way for the subjugation of the country by the Austrians.
During the Lent of 1622 he preached with especial fervour.
He had, however, a presentiment that his laborers would shortly be brought to a close by a martyr's death.