Composed in 1947, Jean Langlais' Suite Médiévale is written in the form of a low Mass, or Messe basse, which followed the pre-Vatican II practice of playing the organ at prescribed times during Mass when the choir was not present. The fourth movement of the suite, a meditation for Communion, quotes two plainsong melodies - the Holy Thursday antiphon Ubi caritas (Where charity and love are found) and Jesu dulcis memoria (Jesus, the very thought of thee.)
Perhaps one of the most beautiful pieces Langlais ever wrote (and the Suite as a whole one of his most successful works), he brilliantly weaves together the two plainsong melodies in a way that is very reminiscent of his own improvisations.