Theory:

Imagery is a technique used in literature. It is one of the several poetic devices used by the poets. Poetic devices are used to create a structure and meaning to the poetry.
So what is the role of Imagery?
Imagery means the usage of verbal images to describe a concept. The goal of using “imagery” is to create images in the minds of the readers. Writers use descriptive words to do that. The poem is said to have imagery if it describes the look, sound, smell, taste, and/or feel of something and these five senses are targeted while creating imageries. It helps the readers understand the literary work better.
So how is this relevant to the poem Beauty?
The poem "Beauty" has several imageries in it. While reading the poem, we can easily imagine the scenes described in the poem. The words such as sun, trees, birds, night, wind sighing, and rain falling are various images in the minds of the readers.
Example:
The first stanza creates an image of scenery with trees, birds, sun, and cornfield in the readers mind.
 
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The second stanza can create images such as a beautiful, cool, and/or rainy night in the reader's mind.
 
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