Although the song of the cricket and the grasshopper have different meanings or functions in relation to themselves, the speaker of the poem refers them to the poetry of the Earth, which could be more broadly defined, metaphysically - or physically, as the sounds of life, which do not cease even in winter. Hence, the idea in the poem that the poetry of the Earth never dies or ceases. The obvious metaphysical connection here is between poetry and life, the songs being the poetry of the Earth. Metaphysics is a broad subject itself. Among the many ways it
has been used are: exploring the nature of being or meaning in the world, meaning which is meta (above) physics. So physical things/functions in the world have their purpose in the mechanistic sense. The metaphysical sense would be to analyze those physical things/functions in attempts to arrive at a more profound meaning, one which transcends the physical implications. As it is often referred to in poetry, this could be the metaphysical conceit, which is a conceptual and/or metaphorical comparison. In this case, the comparison is with poetry itself and the sounds of life; grasshopper and cricket songs. Since these songs, poetry of the earth, continue unabated by the winter, there is also a comparison of immortality (of life in general) and the immortality of poetry itself. Or, to be more precise, the direct comparison is with the creative process: life, songs and poetry.