Another theme in the poem is existence. In line six, the poet explores the meaning of man's existence. The visual expression of life is the unconscious act of breathing. Breathing is an innate action that accompanies birth. The poet refers to mankind's "breathing, in and out," as the essence of existence. The cessation of breath reveals the end of life. This notion of inevitability is captured in the last line of the poem, when the poet recognizes that all who have existed will eventually die.