Bach led the first performance of Darzu ist erschienen der Sohn Gottes, BWV 40, his first Christmas Cantata composed for Leipzig.

Johann Sebastian Bach was a German composer and musician of the late Baroque period. He is known for his prolific output across a variety of instruments and forms, including the orchestral Brandenburg Concertos; solo instrumental works such as the cello suites and sonatas and partitas for solo violin; keyboard works such as the Goldberg Variations and The Well-Tempered Clavier; organ works such as the Schübler Chorales and the Toccata and Fugue in D minor; and choral works such as the St Matthew Passion and the Mass in B minor. Since the 19th-century Bach Revival, he has been widely regarded as one of the greatest composers in the history of Western music.

Darzu ist erschienen der Sohn Gottes, BWV 40, is a church cantata by Johann Sebastian Bach. He composed it in 1723, his first year in Leipzig, for the Second Day of Christmas, and first performed it on 26 December that year in both main churches, Thomaskirche and Nikolaikirche. It was the first Christmas cantata Bach composed for Leipzig. The title of the cantata also appears in more modern German as Dazu ist erschienen der Sohn Gottes.

A Christmas cantata or Nativity cantata is a cantata, music for voice or voices in several movements, for Christmas. The importance of the feast inspired many composers to write cantatas for the occasion, some designed to be performed in church services, others for concert or secular celebration. The Christmas story, telling of music of the angels and suggesting music of the shepherds and cradle song, invited musical treatment. The term is called Weihnachtskantate in German, and Cantate de Noël in French. Christmas cantatas have been written on texts in several other languages, such as Czech, Italian, Romanian, and Spanish.