The Christmas Oratorio occupies a special place among Bach's (1685-1750) great vocal works: it is was written to be performed in the church year of 1734-35 on six festive days spaced across two weeks and at two different. Bach therefore amalgamates the concepts of an oratorio divided into several parts with a cantata cycle embracing the church year. The text of the work and the theme of individual sections largely agree with the content of the gospel extracts associated with the festival: the birth of Jesus, the proclamation of the glad tidings to the shepherds, the adoration of the shepherds, Jesus circumcision and baptism, the arrival of the Magi and finally, the adoration of the Magi.
In its musical material, the majority of the Christmas Cantata can be traced to secular cantatas. By recycling in this way, Bach could preserve music written for incidental occasions by making it part of the church repertoire. When Bach selected the music for the Christmas Oratorio, he laid great emphasis on ensuring it agreed with the parameters of the text (the length of lines and stresses), but also that it fitted expressive musical forms. This is perhaps most evident in the various choruses and arias used from the birthday cantatas (BWV 213 and 214), since the movements celebrating the birth of secular figures can be used simply to depict the birth of Jesus, the King of Heaven. Bach could also recycle certain musical effects when appropriate to the text. The opening chorus – which is drawn from a movement of a birthday cantata – commences with trumpets, drums and violins, and perfectly matches the general expectations of both texts (%u201CExult!”)
We cannot be sure as to the identity of the librettist. It is conceivable that Christian Friedrich Menrici (Picander) lent some of his own secular verses but we do not find his name mentioned on either the manuscript or elsewhere. It does seem highly probably however that Bach collaborated in producing the libretto, the apportioning of the biblical text and the placing of the chorales.
For the movement types, Bach turned to the forms used in his Passions: the biblical words of the evangelist appear as secco recitativo and choruses, as are the manifestations of Herod (No. 55). By comparison the angels (No. 13) are heard supported by a string accompaniment. The church songs are heard in four voice instrumental chorale settings. A rare exception is when the chorale text within a movement is welded with free verses in the shape of a cantus-firmus movement (No. 7), or else appears in an arioso-like setting (No. 38 and No. 40). Bach sets the free texts in the form of an instrumental recitative and aria, in which the recitative functions as a prelude to the aria (these movements are without exception original compositions.) The other form we encounter is the use of choruses. Five sections commence with such a movement – in the second section, it is substituted by an orchestral Sinfonia – but within sections however, this movement type never occurs.
The musical realisation of the different movement types of the Christmas Oratorio is confirmed by the late date of their composition. This can primarily be observed in the subtle textures of the simple four voice chorales, and their loose organisation. Besides the carefully structured tonal scheme of the entire oratorio, other formal elements strengthen the sense of unity of the whole. One such is the orchestration: the identical instrumental forces of the first and last parts are identical (3 trumpets and drums). The re-emergence of the first choral melody in the final movement also emphasises its cyclical character.