I think back to “There’s something quieter than sleep” where she sees the dead body, and I’m imagining her writing about the heart and the spirit leaving the body here. The spirit (in this poem represented as “I”) is eager to move on yet the heart lags behind and the spirit is worried it will be called back to “the natural warmth he gave” of the body. For me the key word here is “pray” in that when the heart is done (as the body dies) it engages in prayer with the spirit so that the spirit can move on.

The previous poem, “I keep my pledge“, speaks of Death not coming for her and so she remains in the natural world of experience (I guess I’m thinking Blake here), and so these three poems form a sort of unity of thought and image where death is a calling to a new world, but there is a pull, a “simple gravity” to remain alive and experience the “light” and “warmth” of this world.