Bach's St. Matthew Passion

I’m still in the midst of listening to all of the music I have by Bach.  Currently, it’s the St. Matthew Passion.  What I’ve found interesting while listening to this is that there are melodies that I recognize because they’re still used in church.  I had the same experience while listening to some of Bach’s organ music (in particular the chorale prelude “Wachet auf, ruft uns die Stimme”).  But, without researching, I don’t know if these are melodies that Bach wrote or merely melodies that he used and arranged for his own devices (judging by the attributions in the hymnal, he did arrange some older melodies for hymns).  Either way, it’s pretty interesting that the same melodies (or variations of them) are still used in churches three hundred years later.