The poem describes many different ways of looking at rain and includes perspectives of people in different situations and occupations: a sick man in his room, schoolboys on the street, a farmer in his fields, and finally the Poet (Longfellow likely means himself, and it is noteworthy that "Poet" is capitalized). The descriptions of the rain can be read metaphorically as the ways in which people see the power, beauty, and benefits of the natural world. Just prior to mentioning the farmer, Longfellow describes the patient oxen in the fields and their reaction to the rain, with a suggestion of the rain emanating from the divine: "their large and lustrous eyes seem to thank the Lord, more than man's spoken word."
The section about the Poet implies that he can see meanings in the rain that may not be observed by others, such as the farmer. By the poem's end, we understand the rain and the water it delivers to all of the waterways serves as a metaphor for the universe and its perpetual motion and change, captured in Longfellow's final line "the rapid and rushing river of Time." Longfellow describes the rain from the perspective of the Seer (who may be a stand-in for the Poet, and once again the term is capitalized), and offers the idea that profound truths about life and our place in the universe can be revealed when we study something as simple as the rain. This final stanza clearly imagines the rain as a broad metaphor within this context, with the rain representing life's cycles or birth and death, Time and the Universe.