"Metaphysical" is an adjective that describes something that transcends the physical world. Metaphysical poets often use complex and concrete metaphors to explore complicated metaphysical ideas—such as death, the subject of Donne's poem.
Readers and critics characterize metaphysical poetry as explorations of complex, highly intellectual thought. The transition and relationship between life and death is certainly complex, perhaps our most complex subject matter as humans. How does Donne resolve the complexity of dealing with death?
For one, Donne offers multiple ways of thinking about death. Perhaps it is a great conjunction, all things living and dying becoming one, as our souls "endure not yet / A breach, but an expansion, / Like gold to airy thinness beat." Or, if we remain as individual units when we die, our relationship to the living is a parallel one, "such as stiff twin compasses are two." To offer competing descriptions of what death may be like does not undermine any one idea but conveys the many nuances of death, the many possibilities as to what it is and how it relates to life.
Aside from its intellectual complexity, this poem encapsulates metaphysical poetry in other ways. For instance, metaphysical poets often use wit or humor. While a metaphysical poem may address such lofty subjects as love, life, and death, its authors frequently reach for levity to ground their poems. In Donne's poem, the entire first stanza comically makes light of death itself:
"As virtuous men pass mildly away,
And whisper to their souls to go,
Whilst some of their sad friends do say
The breath goes now, and some say, No...."
Donne describes death itself as something mundane and breezes through it with no drama or fear. "Men pass," their loved ones are "sad," and they die—it is as quiet and simple as that. It is funny and a bit jarring that the speaker would treat death as such an unimposing everyday matter. Of course, this first stanza of levity sets the stage for the real discussion: what is death like, what is the essential quality of death? Donne offers a couple of possible explanations, but not before jesting about the human tendency to overdramatize death.