Here is a very small history of where this work comes from. I may have gotten a little carried away, but it sure was fun! Enjoy the sounds and the learning!
Martin Luther (not Mr. King, but the reformer from 500 years ago; responsible for Lutheranism and other protestant faiths), believed that church should be an interactive event for the common people as much as it was for clergy and the elite. Because of his influence, churches began to switch from using Latin (an already dead language) to the venacular (the language spoken by the common people) in their services. Therefore, a major point of his reform was to also have music that was singable and easily understood by congregations.
Because Luther was German, Lutheranism became an identifiably German faith. Bound with the tradition of Lutheranism, were several hymn-tunes. These hymn-tunes were familiar to the German people, and Luther and his contemporaries paid special attention to setting texts to these hymns that were easily understood by the commoners. These chorales, or german hymns, became a favorite starting point for the compisitions of Johann Sebastian Bach.
Bach would frequently take an old well-known Lutheran hymn tune (a chorale), and turn it into a multi-movement work called a cantata. The word cantata literally means 'to be sung' as opposed to the word concerto, which meant 'to be played'. This is the chorale that Bach used to craft the corresponding entire cantata. The sopranos sing the chorale "Christ lag in Todesbanden" very near (there are some chromatic alterations) to how it would have been sung 500 years ago. The other parts in the choir sing a harmonization that supports the sopranos and which was written by Bach. The entire cantata "Chirst lag in Todesbanden" is based on this tune. Bach crafts 7 verses with this same tune, but somehow each verse stands independant from another, and each verse is so completely different and interesting, that the performer and the listener never become bored.
Take a listen: