This article examines a letter from Beyhagi s history, based on pragmatic theories. Based on this approach, the context of situation, diexis, including: social, personal, time and spatial diexis are analyzed in the text. In other words, the communicative competence of the writer or his linguistic knowledge and his application of rules in different situations are taken into consideration. Since the communicative competence of the writer is interrelated with his attitude and motivation and in so far as the description of language functions in a text can illustrate some of the linguistic features, not explicitly cited in the text, such analyses may play an important role in our literature. To this end, the segmental elements like words, and sentences as well as  some supra segmental features like stress and intonation are analyzed in the text.