Also called “On the Morning of Christ’s Nativity” or “On the Morning of Christ’s Nativity, 1629” or “On the Morning of Christ’s Nativity, Compos’d 1629.”

https://www.dartmouth.edu/~milton/reading_room/nativity/text.shtml

I wrote a seminar thesis on this once. It’s not just about connecting the birth of Christ to the passion in theological terms. Milton is making a sort of quantum confession: the birth of God in time collapses our reality. The Christmas Day of 1629 becomes, itself, “the happy morn;” the liturgical hymn of Philippians 2:6-8 (and 9-11) is transfigured into Milton’s second stanza; everywhere the light is breaking in, nowhere can the natural order contain the “spooky action” (no longer at a distance).

In other words, John Milton was a genius.