So I read a good chunk of The Walls Do Not Fall and didn’t quite understand what was going on. However,I found this bit of explanation by the one and only Susan Stanford Friedman at http://www.english.illinois.edu/maps/poets/g_l/hd/trilogy.htm, and I think it provides some valuable insight:
The initial experience of the Trilogy is immersion in the harsh reality of the contemporary world. The conditions under which H.D. wrote underline the philosophical starting point of the poem and help dispel the frequent critical notion that H.D. was essentially escapist in her art and too fragile for the modern world. Throughout the war, H.D. remained in London, the center of the air war in Britain. As an American, she could have easily returned to the States. Or she could have taken the urgent advice of her friends who implored her to leave the city for the relative safety of the countryside. .. .
Like the woman Hilda Doolittle, the poet of the Trilogy makes no attempt to escape the gaping walls and constant death that surround her. The poem begins with the poet walking through the ruined city just after a bombing raid. Staring in desolation at the destruction, she records her impressions in the first section. But even as she is immersed in the concrete, actual horror of the war, she refuses to limit her understanding of the destruction to the material rubble in front of her. The ruins remind her of Pompeii–another instance of sudden catastrophe in human experience. This is no escape back into time; rather, H.D.’s comparison foreshadows her insistence throughout the poem that the ultimate reality of any single moment in history is contained in a pattern of essential experience which informs all time. The fire in London, like the fire in Pompeii, is a special kind of flame–Apocryphal fire, destruction which brings rebirth. H.D. approaches external reality in the same way she learned to read the mysterious script of psychical reality from Freud. The rubble contains, she believes, a coded message whose interpretation can reveal an order underlying the surface reality of chaos.
Excerpt from Psyche Reborn: The Emergence of H.D. Bloomington: Indiana University Press, 1981. 102-104. by Susan Stanford Friedman.