This passage is from what is now commonly called Third (or Trito-) Isaiah (Is 56-66). These chapters take up the themes of Isaiah 40-55, which announced the impending return of the exiles from Babylon to their homeland (Is 40), but they reapply these themes to a new situation.
It is no longer the exiles returning to their homeland but the pilgrims going up to the Temple at Jerusalem for the feast (Tabernacles?).
When read at the second Mass of Christmas, these themes are reapplied to the birth of Christ. The passage now speaks of the joy of the new Israel at the advent of its salvation.
Like the other enthronement psalms, Psalm 97 is appropriate for any Christian festival. A different selection of verses from this psalm is used during the Easter season in series C. The present selection includes verses 11-12, with reference to the dawning of the light, imagery that has passed into the lore of the season and is expressed in so many Christmas carols.
This passage is very similar to the second reading at the midnight Mass (Titus 2:11-14). Both passages speak of the “appearance” of divine salvation and can therefore be related fittingly to the Nativity. But there is a difference, too.
The earlier passage went on to speak of the second coming and made it the basis of an ethical exhortation. This passage takes a different direction.
The appearance of “God our Savior” in the Christ event leads to our regeneration and renewal, our rebirth as children of God (see Gal 4:5-7). Christ is Son of God by right; created human beings forfeited divine filiation by the Fall. But Christ has appeared to give us rebirth as children of God.
This thought is succinctly expressed in the collect that Cranmer composed in 1549 for the second Mass of Christmas: “Almighty God, who hast given us thy only-begotten Son to take our nature upon him. ... Grant that we, being regenerate and made thy children by adoption and grace, may daily be renewed by thy Holy Spirit.”
And the Anglican poet Christopher Wordsworth, taking up the great patristic paradoxes of the Incarnation, expressed it thus:
God comes down that man may rise,
Lifted by him to the skies;
Christ is Son of Man that we
sons of God in him may be.
This reading completes the narrative begun in the gospel for the Midnight Mass—the pilgrimage of the shepherds to Bethlehem and their visit to Mary, Joseph, and the babe in the manger.
The angelic message had told them that the things they would see would be a “sign” (Lk 2:12). What they see has a meaning beyond what is visible to the eye, which can only see a baby, its mother, and her husband—a common enough sight. But this sight is a “thing that has taken place.”
The word translated “thing” can also mean “word,” that is, a significant, meaningful communication. So the sight of the child is a sign communicating to the shepherds the significance of what the angelic message had proclaimed: God’s salvation has come to earth.
The shepherds do not see the salvation itself but only its outward sign—the birth of the child, wrapped in swaddling cloths.