January 6 : The Epiphany of the Lord (during the day)
The antiphon traditionally associated with this feast is given in the Missal and Graduale as “We have seen his star in the East, and have come with gifts to adore the Lord.”
The First Reading of the Mass of the Day is Isaiah 60:1-6, which gives a strong indication of a theme of light over the nations, instead of a star over Bethlehem. The Psallite composers went one stage further and took their inspiration from the Office of Readings for the day, which includes the whole of Isaiah chapter 60. In particular they focused on verses 19-20, beginning
The sun shall be no more your light
nor for brightness shall the moon give you light;
but the Lord will be your everlasting light,
and your God will be your glory.
From there it is but a short step to Revelation, chapter 21-22, especially 22:5b-d:
They will need no light of lamp or sun,
for the Lord God will be their light,
and they will reign forever and ever.
It was then easy to establish the canticle as Revelation 21:24-27ac and 22:3b-5, starting with verse 24 for the feast:
The nations will walk by its light,
and the kings of the earth will bring their glory into it.
and the antiphon text adapted from the preceding verse, Revelation 21:23:
And the city has no need of sun or moon to shine on it,
for the glory of God gives it light, and its lamp is the Lamb.
May the glory of God light up our own lives!