Angelus Ad Pastores Ait, a paraphrase of a Biblical text set as a motet by Jan Pieterszoon Sweelinck, is taken from where the angels appear to the shepherds in the field, telling them that Christ has been born. This passage has ben set by a number of composers, but one does not need to know the text to enjoy the remarkable five-part imitative counterpoint with alternate harmonic sections typical of Sweelinck. Sweelinck straddles the line (both chronologically and stylistically) between the Renaissance and the Baroque - and both styles can be heard in single pieces of his music.
The sheet music is published by the TBQ Press - http://www.tbqpress.com/ Scroll down their listings to find the piece.
It is also available as an unpublished brass sextet.
The mp3 performance is from my CD “Savannah River Brassworks,” available on my Recordings page.