Explanation:

Man comes and tills the field and lies beneath,

And after many a summer dies the swan.

Answer: These lines are selected from a famous dramatic monologue, “Tithonus” by Lord Alfred Tennyson. Here the poet describes the misery of old Tithonus.

Tithonus is a very handsome and agile young man. The goddess of dawn Aurora falls in love with him. She takes him to Zeus and begs for immortality for him. What she forgets to want is the everlasting youth for Tithonus. However, Zeus grants her prayer. Aurora keeps him with her. But with the passage of time, Tithonus_grows old. Whereas he does not die like the people of the earth. Now he is miserable. He has lost his physical strength and passion. His blood does not glow at the sight of his dark eyes of Aurora. Aurora is evergreen. She does not lose her beauty, charm, and youth. So she can live with old Tithonus no longer now. Hence Tithonus here cries for a release from-his-accursed immortality. He laments that man comes and works in the fields. He dies at last. He goes on his job till his death and is buried beneath the earth. After many years, the swan dies. It is only Tithonus himself who cannot die.

In fact, we find an elegiac tone here. The sudden death of Hallanm shocks Tennyson most. This deep shock provides him with an elegiac tone which has been expressed in these lines.