Henri du Mont wrote during an unusual time, the period well after the Renaissance, when polyphony and plainsong were common and quite separate, and the pre-Vatican II era, when the high Mass was dominated by noisesome, loud sing-songy tunes in Latin. Du Mont's Messe Royale falls somewhere between plainsong, polyphony, and the pre-Vatican II method. It is not quite plainsong, since it is timed, but follows the notation and pattern. It is not polyphonic properly, since it contains a singular, flowing melody. And it is not of the 1950ish variety due to its time of writing, although it probably has the most in common with these.
Not unlike Josquin de Prez's Missa Pange Linguae, the Messe Royale begins each setting of the Ordinary with the same melody, although unlike Josquin the Messe Royale does not explicitly borrow from an extant Gregorian melody, unless a uniquely Gallican tune escapes me. In fact each part of the Messe Royale begins with the same melody, which over the course of the Mass becomes repetitive.
It is not an especially fine Mass, but the Kyrie for the Messe Royale as interpreted by the choir of Saint Just, the FSSP parish in Lyon, is very special. Saint Just offers a rendition of this Kyrie, intended for the private chapel of Louis XIV, with a mix of Old Roman droning and the French style of organ Mass. Despite mixing the eighth and eighteenth centuries, it works extraordinarily well and is quite moving. The domineering presence of God that this sort of music proclaims mimics the song of the angels (it is the remembrance of Saint Michael's apparition today) and might compel some to put down their hand Missals and just think about God for a moment. I would like to hear a happy Gregorian or polyphonic Gloria after this Kyrie, but this sort of music absolutely has a place and offers ambitious choirs something to aspire to after perfecting the seasonal settings of Mass. One does not need to sing Palestrina for special occasions. This sort of music will do.
On another note, I will be in London and Oxford for the next two weeks and happily away from my computer. J and Fr. Capreolus will keep the posts and comments rolling, so don't stop reading. Please keep me in your kind prayers.