Tomorrow is the second Sunday of Advent.
When Bach worked in Weimar, he wrote a cantata for each of the 4 Sundays in Advent. However in Leipzig, music (other than chorale singing) was not allowed in the churches in the period between the first Sunday of Advent and Christmas Day. In order to still use (and show off?) the Weimar Advent cantatas in Leipzig he reworked and expanded most of them for other times of the church year in Leipzig.
He truly mastered this rewriting process with cantata 70, Wachet! betet! betet! wachet!, originally written for 2nd Advent in Weimar in 1716, but now dramatically expanded for the 26th Sunday after Trinity, November 21, 1723.
Read much more about the reworking process and about this particular cantata in this Weekly Cantata post from 2016, which now includes a new link to the excellent live video performance by the J.S. Bach Foundation.
Wieneke Gorter, December 7, 2019.