Just a little about Johann Bach, Cantatas, and Advent....nothing deep.
Bach has something of a special hold on a form of music called "cantatas". Cantata comes from the Italian "cantare" or sung, to sing, vocal (think cantor in the Temple). The Lutheran church year is divided up into the church seasons with Advent (now) leading into Christmas (which doesn't start until Christmas Day by the way so Happy Advent is the apropos greeting) and the rest of the year (Lent, Easter, stuff like that).
Just about every Sunday while Bach was a church musician he and his choir and orchestra performed a cantata - mostly of his writing. These aren't little dinky works or pieces of music that were performed outside the service. They were part of the service itself - the musical framework. There are two major collections or series of these called the Bach Jahrbuchs - Bach's Yearbooks, written in the 1710s that are of the one after another set. Write it, rehearse it, perform it on Sunday and start a new one for the following week - for two years worth.
They were of no set number of movements but usually of an "odd" number of individual pieces 5 or 7 and in what "scholars" call Chiastic Form - They had an opening movement, usually a chorus, followed by 1 or 2 soloist movements and then a center or "center of the cross" movement which was often a chorus, 1 or 2 more soloist movements and a concluding hymn. All were composed according to the appropriate scriptures for the day so they were mirrors of the church service itself. On the eve before the first Sunday in Advent (Christmas falls on a Saturday so that next Sunday the 26th is the Second Day of Christmas), there are about 200+ cantatas that survived the 300 years and this selection is from that one, "Nun komm, der Heiden Heiland" (original: "Nu kom der Heyden heyland", English: "Now come, Saviour of the heathens")
It was written in 1714. Bach was 29 years old at the time. He had buried one wife, had a second wife, a gaggle of kids and as he said "I workd hard" when asked about his life.