This paper offers new insights into the philological and linguistic investigation of the earliest Old Church Slavonic (Old Bulgarian) translation of Gregory of Nazianzus’ Homily 38 “On the Theophany” (Εἰς τὰ Θεοφάνια, CPG 3010.38; BHG, 1921-1921b; PG 36, 312A-333A). This anonymous ecclesiastical sermon is transmitted by two manuscripts: one of East Slavic provenance (St Petersburg, Russian National Library, Q.п.I.16, second half of late 11th century), while the other is of South Slavic origin (Sofia, SS. Cyril and Methodius National Library, № 674, mid-14th century). The work comprises two main parts. First, it presents a text-critical analysis of the textual transmission, demonstrating that the surviving codices derive from a common archetype. Second, it provides scholars with a study of the language and of some aspects of the translation techiques, offering compelling evidence of both a marked analogy with the Didactic Gospel of Constantine, Bishop of Preslav, and of the presence of a number of lexical and grammatical archaisms. These features suggest the translation likely dates to between the late 9th and early 10th centuries, a period prior to the consolidation and standardisation of the Preslav school’s literary norm. The paper’s second part contains a new, significantly revised critical edition of the Old Church Slavonic translation of Homily 38.