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).
Passions and Oratorios of the first half of the 18th century
Jesus Christus ist um unsrer Missetat willen verwundet is a St Mark Passion which originated in Hamburg in the first decade of the 18th century. Johann Sebastian Bach's first staging of this Passion music was in Weimar 1712. Its vox Christi bass appears in secco and accompagnato recitatives, and in an arioso on the Gospel words "Eli, eli, lama asabthani". In his Brockes Passion George Frideric Handel set Jesus' words for bass in recitatives, ariosos and arias. The Evangelist's recitatives are set for tenor.
In Bach's extant Passion compositions the vox Christi bass combines with an Evangelist's tenor voice. The Evangelist narrates the story in the Gospel's exact words in recitative secco. In the St John Passion the words of Jesus are set as recitatives secco leaning toward arioso. In the St Matthew Passion they are in accompanied recitative, that is they are additionally highlighted by an accompaniment of strings and basso continuo. The Vox Christi also appears in Bach's Christmas Oratorio, and in his Ascension Oratorio.
Bach's cantatas
In Bach's church cantatas the vox Christi may utter either literal words from the Bible which are neither direct quotes of or even attributed to Christ but are presented in the context of the musical work as being made by Christ, or extra-biblical words, for example in a dialogue between the Bridegroom (Christ) and the Bride (the Soul), or in an address to the Bride.
In Bach's Weimar cantatas (1714–1716): In Himmelskönig, sei willkommen, BWV 182, (25 March 1714), Bach's first cantata in Weimar, for Palm Sunday coinciding with Annunciation, verses from a Psalm are treated as if Jesus said them, set as the only recitative of the cantata, expanding to an Arioso: "Siehe, ich komme, im Buch ist von mir geschrieben" ("Lo, I come: in the volume of the book [it is] written of me, I delight to do thy will." . In Erschallet, ihr Lieder, erklinget, ihr Saiten! BWV 172 (20 May 1714) for Pentecost the bass sings the words of Christ from the Gospel of John: "Wer mich liebet, der wird mein Wort halten" ("If a man love me, he will keep my words: and my Father will love him, and we will come unto him, and make our abode with him." . In Nun komm, der Heiden Heiland, BWV 61, (2 December 1714) the bass sings the words of Christ from the Book of Revelation: "Siehe, ich stehe vor der Tür und klopfe an. So jemand meine Stimme hören wird und die Tür auftun, zu dem werde ich eingehen und das Abendmahl mit ihm halten und er mit mir." ("Behold, I stand at the door, and knock: if any man hear my voice, and open the door, I will come in to him, and will sup with him, and he with me. " . In Barmherziges Herze der ewigen Liebe, BWV 185, (14 July 1715), the bass summarizes admonitions from the Sermon on the Mount, all introduced by the keywords "Das ist der Christen Kunst" (That is the Christian art). In Bereitet die Wege, bereitet die Bahn, BWV 132, (22 December 1715) the question Wer bist du? (Who are you), posed to St. John in the Gospel, is given to the bass, as if Jesus asked the listener this question. In Mein Gott, wie lang, ach lange? BWV 155, (19 January 1716) serious questions get answered by words of consolation, sung by the bass as the vox Christi, almost as an arioso on the words "Damit sein Gnadenlicht dir desto lieblicher erscheine" (so that the light of His grace might shine on you all the more brightly).