Originally, the second Mass of Christmas went together with Lauds. The antiphons of Lauds form a kind of call and response, or question and answer cant about the experience of the shepherds coming to find the Christ Child. Sometimes the Second Mass of Christmas is nicknamed the "Mass of the Shepherds" and we call it by the name of the Introit as well. Lux fulgebit (Isaiah 9 with Ps 92).
Da nobis, quaesumus, omnipotens Deus:
ut, qui nova incarnati Verbi tui luce perfundimur;
hoc in nostro resplendeat opere,
quod per fidem fulget in mente.
This is an ancient prayer, found in manuscripts of the Gregorian Sacramentary, such as the Hadrianum and Paduense. It survived the experts of Bugnini’s Consilium to live on in the same moment in the Novus Ordo.
Your Lewis & Short will enlighten you that perfundo is "to pour over, to wet, moisten, bedew, besprinkle". But it comes to mean also, in a poetic sense and in post-Augustan prose, "of the sun’s beams or fire, to flood or fill". Thus it also means "to imbue, inspire, fill with any thing", as with joy or with fear or with awe.
The theme of light plays through all the texts of this Mass, as it does, but in a different sense, in the Mass in Nocte, Dixit Dominus. Playing out through the Mass is the rising sun and the shepherd’s at the manger.
Light in the morning shines through the Mass, as it does right at this moment of writing for me – the sun streaming into the window its low beams in the depths of winter as it rises far toward the south and late in the morning. Remember also that in the Introit, though we have just a snippet of the Ps 92, we are supposed to remember from that single line the whole of the psalm. Monks could do that. Pious Jews could do that. We should at least look up the psalms cited in the verses of the Antiphon and consider what the Church is saying to us by citing it.
Opus is certainly work or labor, but it goes a bit farther to embrace alse "action" or "business" in the wider sense of all we do outwardly.
We beseech You, Almighty God, grant to us
who are bathed in the new light of Your incarnate Word;
that this which gleams in the mind through faith,
may shine brightly in our action.
Note all the "light" words.
Briefly, there is a play between the inward and the outward. Light can shine in our eyes and it is very visible. But sacramental grace is "insensible", but its presence in us is known to others by our outward deeds.
Latch into that word perfundimur, "we are bathed" in new light. This sounds like baptism, in a sense.
Also, we ask God to illumine our faith. In this life we walk in darkness. We see through St. Paul’s glass, "darkly". In heaven we will not have faith, but rather knowledge. But there are those moments of realization, when we have encountered mystery when we we have a transforming or illuminating experience which, as a consequence, changes us in ways that are discernible in our outward lives and inward peace.
Also, remember from all eternity the Word, the Logos, was the perfect invisible image of the invisible Father God. In the incarnation he becomes the perfect visible image of the invisible God. We are images of God. In our words and deeds, that image should shine in us so that others may see it.
We ask for transforming graces. But in receiving them, we can be a shining mirror, though still dark and cracked in places it is admitted, to reflect God’s light to others.
There is so much more to say about this oration, and all the others, but that’s what I have time for before I dash off.