I and III are written in the keys of D major, part II in its subdominant key G major. Parts I and III are similarly scored for exuberant trumpets, while the Pastoral Part II (referring to the Shepherds) is, by contrast, scored for woodwind instruments and does not include an opening chorus. Part IV is written in F major (the relative key to D minor) and marks the furthest musical point away from the oratorio's opening key, scored for horns. Bach then embarks upon a journey back to the opening key, via the dominant A major of Part V to the jubilant re-assertion of D major in the final part, lending an overall arc to the piece. To reinforce this connection, between the beginning and the end of the work, Bach re-uses the chorale melody of Part I's "Wie soll ich dich empfangen" in the final chorus of Part VI, "Nun seid ihr wohl gerochen"; this choral melody is the same as of "O Haupt voll Blut und Wunden", which Bach used five times in his St Matthew Passion. The music represents a particularly sophisticated expression of the parody technique, by which existing music is adapted to a new purpose. Bach took the majority of the choruses and arias from works which had been written some time earlier. Most of this music was 'secular', that is written in praise of royalty or notable local figures, outside the tradition of performance within the church. Instrumentation The scoring below refers to parts, rather than necessarily to individual players. Adherents of theories specifying small numbers of performers (even to 'One Voice Per Part') may however choose to use numbers approaching one instrument per named part. Part I 3 trumpets, timpani, 2 transverse flutes, 2 oboes (both of which double on oboe d'amore) 2 violins, viola, continuo group Part II 2 flutes, 2 oboes d'amore, 2 oboes da caccia, 2 violins, viola, continuo Part III 3 trumpets, timpani, 2 flutes, 2 oboes (both of which double on oboe d'amore), 2 violins, viola, continuo Part IV 2 horns, 2 oboes, 2 violins, viola, continuo Part V 2 oboes d'amore, 2 violins, viola, continuo Part VI 3 trumpets, timpani, 2 oboes (both of which double on oboe d'amore), 2 violins, viola, continuo Notes Parts and numbers Each section combines choruses (a pastoral Sinfonia opens Part II instead of a chorus), chorales and from the soloists recitatives,