So whence cometh the addition of the word one into the formula? It is present in the old, bad, ICEL rendering. But it has an earlier history than that, as Sons and Daughters of the Anglican Patrimony will be clamouring to explain. And that is why one is present in the Ordinariate Divine Worship Missal (which, incidentally, will not be affected by George's decree).
I think English worshippers will first have met it on Whit-Sunday morning n 1549. They heard, at the end of the perpetual memorial pro Rege near the start of The Supper of the Lorde and the Holy Communion, commonly called the Masse. "... Through Jesus Christe oure Lorde, who with thee, and the holy ghoste, liveth and reigneth, ever one God, worlde without ende. Amen."
In fact, the literate but combustible Cranmer did 'the 1549 book' in a great hurry, and there are a lot of different versions of this formula. Most often, however, he simply wrote "liveth and reigneth etc.." leaving the rest to the celebrant (these "etc" collects stayed thus until 1662). In fact, a few seconds earlier, in the Pentecost collect, the bemused congregations will have heard " ...who liveth and reigneth with thee, in the unitie of the same spirite, one God, worlde without ende."
That Whit-Sunday experience of Cranmer's incomparable prose led, of course, directly into the Western Rebellion and the consequent Tudor genocide. But that is not today's story.
Why did he add one or Ever one God? Perhaps we should remember the Athanasian Creed, thus translated by Cranmer: "So the father is God, the sonne God: and the holye gost God. And yet they are not three Goddes: but one God". After the enumeration of the Three Persons, perhaps Cranmer felt it appropriate to make clear that "the whole three persones: be coeternall together and coequall."
We should remember that the unLatinate would not have the grammatical number and case of Deus to guide them into realising that it is 'in agreement with' the antecedent qui.
I do have a further suggestion.
Cranmer had a genius for being able to recall in English, not only the sense, but also the sounds of his Latin originals. Vere dignum et iustum est became It is very meet and right ... And monosyllabic God is less euphonious, and less easy to sing to the traditional notes, than ever one God.
None of this affects me personally. I do not say the Novus Ordo, either in Latin or in English. But there is one final oddity about George's decree which I will share with you.
" ... in the unity of the Holy Spirit, God ..."
As I wrote a few moments ago, we, the Latinate, know what Deus refers back to, bcause of things like case, gender, number, drilled into us early in life. But there may yet be people without our educational advantages ... people in remote peripheral places beyond the reach of World Beating education and m'tutor ... little gatherings of whitewashed cabins at the ends of muddy tracks ... where the only visitor is ever the green An Phost van ... the rich peat smoke rising from the chimneys ... the sort of spot that is for ever quintessentially Cork or Kerry or Kensington ...
In such idyllic spots, the unLatinate peasantry, ungrammared though simple and wholesome, may be misled by George and his "Holy Spirit God" into thinking that "God" qualifies, not "Your Son", but "Holy Spirit".
I think we may be in a slightly Oops situation ...