Johann Sebastian Bach’s Christmas Oratorio was first performed in Leipzig at six services between Christmas Day 1734 and Epiphany 1735. Many of its choruses and arias came from secular works he had written earlier. The opening chorus, for example, comes from a cantata performed on 8 December 1733 for the birthday of the Electress of Saxony. Reusing music in this way, the Parodieverfahren, was not unusual in Bach’s time. It was not a simple copy. Bach moved the pieces into other keys, changed the instruments and gave the new words a new musical meaning in several places.