This paper examines the correspondence between fifteenth-century Cremonese nuns and Bianca Maria Visconti, their patroness, in order to investigate the role of religious discourse in the construction of a discourse community. Based on a corpus of letters produced in monastic and conventual contexts, the study focuses on opening and closing formulae, blessings, expressions derived from Deo volente, and religious references embedded in the body of the letters. The analysis shows that these elements, although often formulaic, do not merely fulfil devotional or rhetorical functions; rather, they contribute to defining social roles, power relations, and socio-affective bonds within the framework of patronage. The language of faith and religion is thus used as a pragmatic resource to create proximity, reinforce common ground between senders and addressee, and mitigate requests that may constitute face-threatening acts. From a methodological perspective, the paper also discusses the notion of discourse community in relation to the concepts of community of practice and textual community, highlighting the relevance of linguistic and pragmatic analysis for the study of social networks and sociolinguistic dynamics in historical perspective.