It illustrates a change in the natural environment that the speaker implies is responsible for the growing misgivings described in the text.

It establishes an example of consistency in the natural landscape that the speaker then contrasts with the unpredictability of human emotions.

It presents an observation of an occurrence in the natural world that the speaker then expands on to convey a sense of a turbulent interior state.

It evokes the ordinariness of an event in nature to suggest that the critical self-evaluation the speaker engages in is a common pursuit.