The analysis of the 19th-Century rendition of „Little Office” indicated that in comparison to the contemporary text of the devotion the religious language has not undergone major changes. In the historical text there are only a few features not present in contemporary prayers. These include: – é in affixes -éj in singular genitive and in affix -ém in singular instrumental and locative cases in the adjectival and pronoun declension; – differences in creating past participle with suffixes -one, today inflected as -ęte; – affix ą in singular accusative of feminine nouns, today inflected as -ę; – affix -m in first-person plural verbs, today inflected as -my. Similarly, vocabulary that today is classified as archaic has been preserved in contemporary prayers. The immutability of religious language is one of its fundamental features that has been in force in the Catholic Church until the Second Vatican Council.