This 2nd movement is of the hymn "Adoro te". From Catholicculture.org:
“Godhead here in hiding, whom I do adore; masked by these bare shadows, shape and nothing more.” The text to this hymn of thanksgiving and adoration belongs to St. Thomas Aquinas (1225-1274), and its most famous English translation to Gerard Manley Hopkins (1844-1889). The chant itself is of unknown origin from the first millennium. It is brighter and lighter than many chants, with a smooth and lyrical line of four easy phrases, with a swell in the third phrase that provides quiet drama while never losing its discipline.
Aquinas is said to have written this text at the request of Pope Urban IV for the Feast of Corpus Christi in 1264. This chant is often used as a prayer of thanksgiving after Mass, though it is suitable for any time of focus on the Blessed Sacrament. The Hopkins translation is beautiful; consider the last line of the third verse: “Truth himself speaks truly or there’s nothing true.” But it cannot compare to the lyric quality of Aquinas’s Latin: “Nil hoc verbo veritatis verius.”
Unusual and colorful registration -Gambe or Salicional in the hands, PD 2' with petitie mixture (in this case, coupled from the Recit)