There is no rose of such virtue
As is the rose that bare Jesu.
For in this rose contained was
Heaven and earth in little space.
By that rose we may well see
That He is God in persons three.
The angels sungen the shepherds to:
Gloria in excelsis Deo.
Leave we all this worldly mirth,
And follow we this joyful birth.
Alleluia, res miranda,
Pares forma, gaudeamus,
Here's a video of this song; it's an anonymous 14th-century English carol (original words here):