Lumen de lumine
Today's O antiphon calls Christ the Sun of Justice and the Dawn. Here, he is shown with light radiating from him, for he came to enlighten all men, to free us from the darkness of sin and ignorance giving us a knowledge of Himself.
The ox and ass are present to remind us of Isaiah's prophecy: "The ox knows its owner, and the ass its Master's crib; but Israel does not know, my people does not understand" (Isaiah 1:3).
Detail from a parclose screen by Sir Ninian Comper in Southwark Cathedral, uploaded to accompany this article I wrote.