JS Bach
The Christmas Oratorio
A musical, cultural and spiritual exploration
Markus Rathey: Johann Sebastian Bach's Christmas Oratorio: Music, Theology, Culture
Daniel R. Melanesien: Listening to Bach: The Mass in B Minor and the Christmas Oratorio (print, kindle, audio)
Bach cantatas (a very comprehensive website) https://www.bach-cantatas.com
Bach performances (incomplete but of the highest quality) https://www.bachvereniging.nl/en