This article examines the Latvian language as found in the manuscripts of the Moravian Brethren from the 18^th and early 19^th centuries, offering a sociolinguistic analysis of how standard written Latvian evolved in interaction with spoken dialects. It traces the historical development of Latvian written language from the early Reformation texts to the emergence of a more standardized form following the 1739 Bible revision. Special attention is given to the role of the Moravian Brethren in expanding literacy among Latvian-speaking peasants and fostering a manuscript tradition that included both translated and original religious, didactic, and personal writings. The study analyzes linguistic features at the orthographic, phonetic, morphological, syntactic, and lexical levels, highlighting both adherence to printed language norms and the influence of Vidzeme dialects. German influence is also significant, especially in syntax and vocabulary. The article concludes that the Moravian Brethren manuscripts represent a crucial link between the clerical elite’s written Latvian and a broader vernacular literary culture, thereby contributing to the formation of Latvian as a medium of self-expression, education, and identity.