Final answer:
The literary device used in the third line of the excerpt is a simile.
Step-by-step explanation:
The literary device used in the third line of the excerpt from the poem "I Am Offering This Poem" is a simile. A simile is a figurative language device that compares two different things using the words "like" or "as." They enhance descriptions, making them more vivid and relatable. Examples include "as brave as a lion" or "runs like the wind," creating imaginative and evocative comparisons.
In this case, the author compares keeping the poem to a warm coat when winter comes or to a pair of thick socks that the cold cannot bite through. This comparison helps to create a vivid image in the reader's mind and conveys the idea that the poem can provide comfort and protection.