The Epistola Fundamentalis by Bartholomaeus Holzhauser is a neglected gem of the Counter-Reformation. With pastoral warmth and passionate rhetoric, Holzhauser encourages his fellow-priests to courage and perseverance. For scholars, this text is a key primary document for mid-seventeenth-century inter-Catholic conflict in Europe and is also a fascinating example of Latin being used as a language of original and creative literature in the Early Modern period. For everyone, Holzhauser calls all his readers to be faithful to the tasks before them and give no thought to suffering or the insults of others. This is the first critical edition of the text, accompanied by an English translation, detailed commentary and introduction.