Interestingly this poem is better known in some places by the title of "The Night Before Christmas." There is no group for this poem, so I have moved it to the Poetry Group of enotes.
Personification is when an inanimate object is given human qualities or appearance, and we can see this in line thirteen, which you have identified as containing an example of personification. Let us just remind ourselves of what the line says:
The moon on the breast of the new-fallen snow
Gave the lustre of mid-day to objects below,
We can see that by describing the "new-fallen snow" as having a "breast," that the author is personifying the snow, comparing it to a human and allowing the author to develop his description of the site that he is describing.