Vox Christi, Latin for Voice of Christ, is a setting of Jesus' words in a vocal work such as a Passion, an Oratorium or a Cantata. Conventionally, for instance in Protestant music of the Baroque era, the vox Christi is set for a bass voice.
In Protestant Germany the words of the vox Christi are in German: when the vocal work contains a sung Gospel reading, such as in Bach's Passions, the words are taken from Luther's Bible translation, but the words may also be free verse, as for instance in the Brockes Passion. In either case the composition may also contain a setting of an Evangelist's words, which are traditionally set for a tenor voice.
Apart from a difference in voice type, settings of Jesus' words in recitatives can be further differentiated from surrounding text settings by, for instance, giving them a more arioso character, or setting them accompagnato (while the Evangelist and other characters sing secco).