The present paper explores the historical and exegetical context of Luther's trinitarian exposition of the plural form of the adjective qualifying the generic name of God in Deuteronomy 4:7. Granted that Deuteronomy 4:7 utilises only one of several plural forms applied to the Divine and adduced by Luther as proof of the presence of the trinitarian concept within the Hebrew Bible, the function of that biblical passage in his trinitarian argumentation from the Tanakh was examined. To display typical features of Luther's use of Hebrew scholarship in favour of the Patristic trinitarian and christological doctrines, his statements about the reliability of the Masoretic vocalisation were outlined and his views on the Jewish religion and on the Jewish people were discussed.