I felt a Funeral, in my Brain Stanza III

Lines 9-10

And then I heard them lift a Box
And creak across my Soul

• The funeral service is over. How do we know? Because now the mourners have picked up the casket ("Box") so that it can be buried.
• Here the environment of the poem moves into spiritual territory, as announced by the word "Soul."
• The Soul, apparently, is the floor or ground where the funeral is being held. The word "creak" leads us to think that the Soul must be made of wood – old, creaky wood.

Lines 11-12

With those same Boots of Lead, again,
Then Space–began to toll,

• The mourners who carry the casket seem to be wearing boots made of lead, a very heavy metal.
• After they have walked across the speaker's soul, "Space" begins to "toll" like a bell. Church bells often toll at the end of a service, so we're still in religious territory here. She imagines that her mind or soul is like an entire universe containing a vast empty space.
• Moreover, why does the speaker say, "those same Boots [...] again" as if she knows them already? She recognizes the boots from some earlier experience.