The speaker of the poem describes the filling station from a distance. Given the detailed descriptions of the scene, it is like an imagist poem, a specific description of a place or some visual. This is one stylistic device: using a poem as a painting, combining the visual with the verbal.
Another device Bishop uses is a kind of self conversation. Although the poem starts out as a visual description of a scene, it becomes the speaker's conversation with herself. When she begins to ask questions about the scene, she does three things: begins the conversation with herself, indirectly addresses and engages the reader with such questions, and finally she begins to reassess her initial impressions of the dirty gas station.
In the final stanza, she supposes some answers to her own questions. Once she notices the doily and the other cleaner objects, seemingly so out of place, she considers the entire scene with more humanity and compassion.
Somebody embroidered the doily.Somebody waters the plant,or oils it, maybe. Somebodyarranges the rows of cansso that they softly say:esso—so—so—soto high-strung automobiles.Somebody loves us all.