The title of this poem tells us that the poem is an epitaph, or a text written in memory of a person. The very nature of the poem as an epitaph means that it is part of the tradition of thinking about life, consciousness, and existence in the face of death. This poem is proof that language is not defeated in the face of death, but rises up to meet and interpret it upon every death we talk or write about.
They buried her in the family tomb (1)
This quote takes us through one of the inevitable parts of living in modern society: funerals and tombs. Though cremating is rising in prominence, the tradition of burying loved ones, sometimes in family tombs, is significant in human history. It's our way to take time to think about not only a person's death but also their life and the meaning of existence in general.
and in the depths the dust of what was once her husband trembled: (2-4)
These lines reflect on the idea that from dust we came and from dust we will return. All we are may be just a brief interval between being dust. Yet this dust is not very dead. It senses the return of its wife and trembles. Perhaps, it shows that love and companionship endure, making that brief interval between being dust very much worth it.
joy for the living is sorrow for the dead (5-6)
These lines speak the most specifically about life, consciousness, and existence than any other lines in the poem. Yet the thing is, depending on how you read them, they can be taken to carry many meanings. They can provide solace for sorrow, showing that yes, existence results in death, and death is sad, but only because of the joy we feel in life. So existence is only sad because it's joyful. We wouldn't be sad to die if we weren't happy to live. Yet the lines are arranged with the end note falling on sorrow, which could mean that the poem is a little more depressing—all joy must end in sorrow at the ceasing of that joy. But we'll be getting onto that more in the themes section about "Sadness."