The organ Chorale of J.S. Bach "Wachet auf, ruft uns die Stimme" (BWV 645), performed by Rodney Gehrke on the Flentrop organ from All Saints Episcopal Church in Palo Alto, California; HD 4K video from Voices of Music.
Bach's chorale setting features music from his cantata BWV 140 which was performed in Leipzig on November 25th, 1731. Originally intended for the 27th Sunday after Trinity, the work is now heard most often in Advent. In 1747, Bach commissioned Johann Georg Johann Georg Schübler to engrave six organ chorales for publication—Bach loved to present his works in groups of six; Schübler engraved the books in Zella, in the forest of Thuringia.
Bach based his work on a hymn by Philipp Nicolai. When Nicolai was pastor in Westphalia, the plague killed many of his parishioners; Nicolai wrote a collection of meditations and two hymns in their memory: Wachet auf, ruft uns die Stimme, and Wie schoen leuchtet der Morgenstern. Bach's counterpoint provides a perfect accompaniment for the chorale melody.