Here is the first prayer for the Mass of 23 December, the last full day of Advent before the Vigil of Christmas.
Omnipotens sempiterne Deus,
nativitatem Filii tui secundum carnem
quaesumus, ut nobis indignis famulis tuis
misericordiam praestet Verbum,
quod ex Virgine Maria dignatum est caro fieri,
et habitare in nobis.
This is an ancient prayer from Rotulus 24 published with the Veronese Sacramentary.
Almighty everlasting God,
as we are discerning that the Nativity of Your Son according to the flesh
we beseech You, that the Word grant mercy to us Your unworthy servants
for it deigned to be made flesh from the Virgin Mary
and dwell amongst us.
That use of dignatum est isn’t very common, and so it should spark interest right away. In looking around for how this has been used by ancient writers, I found an interesting passage in a letter of Fulgentius of Ruspe (ep. 7.18):
Deus ergo factus est Christus ut Christus esset deus homoque perfectus, quia verbum dignatum est caro fieri, ut caro posset verbi, hoc est dei, nomine nuncupari. … God therefore became Christ so that Christ might be the perfect God and man, for the Word deigned to become flesh, so that flesh could be proclaimed by the name of the Word, that is God’s.
Nuncupo, as your own copy of the Lewis & Short Dictionary will tell you, is not merely "to call by name, to call, name",, but also "to name publicly before witnesses as one’s heir" and "to announce publicly, proclaim formally". The naming is critically important here. The Word becoming flesh resounds. It is God’s manifest claim of paternity over humanity, an indestructible bond.
What catches my attention in the Collect is the interplay between the form of indignus with dignatum est.
We are unworthy (nos indigni) but it was deemed a worthy thing (dignatum est) that the Word should become flesh (Verbum caro fieri).