In "A Visit from St. Nicholas," is it snow or moon that is the subject of personification on line 13?Previously, ACCESSTEACHER, argued it is the...

Personification is a literacy device in which an inanimate
object is given human characteristics. The lines you're asking about from this poem are
these:

The moon on the breast of the new-fallen
snow

Gave the lustre of mid-day to objects
below,

Clearly, the inanimate object that the author is assigning
human characteristics is the snow. The moon is shining on the "breast" of the new-fallen
snow. It is true, as you state in your question, that only the moon can shine light on
objects below. However, shining light is not a human quality; we don't glow. We have to
use another object to shine light on something. Humans do, though, have breasts--but
snow does not. Therefore, the thing being personified here is the
snow.

I hope that helps.