What are the themes in “A Postcard from the Volcano”?

Stevens' “A Postcard from the Volcano” expresses an idea that life is, in the most basic and most dynamic ways, always experienced the same way. To be alive, the poem suggests, always feels the same. There is a commonality to the experience of life. Yet, those who are living do not identify with those who once lived (and who are now dead).
The narrator reflects on this imaginative wall or breach in the opening lines of the poem, lamenting that “Children picking up our bones/Will never know that these were once/As quick as foxes on the hill” and thus never make the imaginative connection that those who lived in the past were as alive then as any person or creature that is alive in the present.
The poem’s central focus is the breach or failure of imaginative connection between the children living in the present and the narrator’s "we" who lived in the past. Stevens' poem articulates the nature of this breach by depicting how the ways “we saw” and the things “we said” about a particular mansion-house are essentially identical to what the children alive in the present see and say about the same mansion. Life, as it was lived in the past and as it is lived in the present, is lived/experienced with equal vigor, an equal sense of mystery and wonder and even with an equal sense of being somehow haunted by history.