It finds its theme in the great heat and light of the noonday (hora sexta, or sixth hour of the day) sun, and prays the Almighty Ruler to take from the heart the heat of passion. Baudot ("The Roman Breviary", London, 1909, 34) thinks the hymn "probably" by St. Ambrose: "We know, moreover, that the hymns for Vespers, Terce, and None (probably also the hymn for Sext) are his." Perhaps, however, Baudot refers to other hymns ascribed to the saint by Bäumer ("Geschichte des Breviers", 1895, 135). Whatever probability attaches to the hymns for Terce and None affects equally that for Sext, none of the three being found in the oldest Benedictine cycle, while all three are found in the later Celtic cycle. (For discussion of authorship, see Rerum Deus Tenax Vigor).
It is interesting to note that the second stanza is in rhyme throughout:
Luigi Biraghi thinks the rhyme merely a matter of chance; Piedmont thinks it deliberate, but finds no sufficient reason in this fact for denying it to St. Ambrose. Johner ("A New School of Gregorian Chant", tr. New York, 1906, 55) selects the first line to illustrate his contention that whilst in ordinary speech anyone would pronounce the line Réctor pótens vérax Deús, a singer commits no fault in stressing as Rectór poténs veráx Déus. "In German (or English), this kind of thing is impossible. But that does not give us a right to forbid the composer of Gregorian melodies to make use of this and similar licenses. We Germans (and English-speaking people) frequently pronounce Latin with such an exaggerated accent that the words fall too heavily on the ear. Other nations, like the French, pronounce the words more smoothly, with a lighter accent." (For the full argument, see pp. 55, 56.)