When Juozapas Mykolas Karpis became bishop of Samogitia, he published Epistola pastoralis – pastoral letter for clergy and seculars. In historiography it is known for its religious and ethnographical things and even to specialists in Lithuanian philology. However, it becomes the main object of this article because of the purpose to settle what kind of Samogitian diocese he wanted to create and how many influences for this process had his political activity. In the preface shortly introduced the concept of pastoral letter and its origin. Also, is given short descriptions of first pastoral letters in Grand Duchy of Lithuania. In the first section introduced J. M. Karpis life details needed for the research. It helps to reveal future bishop experience, which could have influence, direct and indirect, for letters creation. In the second section and its subsections introduced some communities and problems descriptive in pastoral letter, through which reveals not even Samogitian episcopate situation, but and J. M. Karpis purposes in this diocese.