The angélus is the bells-ringing of the evening that, in the past, marked the end of the working day.
The piece begins with an impressionistic and soft carillon on a flute 4 alone (no mutations). The folk song itself begins at 0'57 and is a traditional "Ave Maria" from Brittany. In the end, the bells become louder, with the hymn surimposed and finally all goes back to the silence of the evening peace with some soft echoes of the bells.
It's unmistakebly Langlais :-)