The taunting voice at the wall is the lower self mocking the higher, and the men who sit on the wall are the faculties poised on the boundary between the inner city and the outside, guarding the border of a person under siege. To eat one's own dung and drink one's own piss is to be forced back onto the exhausted waste of the lower nature, made to live on what the self has already used up and cast off. Rabshakeh, whose name carries the sense of chief cupbearer, is the coarse outer power pressing the awakened self to feed on its own refuse rather than on higher nourishment. This is the mind under threat, jeered at and driven to consume the spent leavings of appetite. The pressure of the lower nature would reduce a person to living on nothing but its own worn-out remains.
Wall: the boundary of the inner city, the border of a person where the guarding faculties sit under siege.
Men upon the wall: the watching faculties stationed at the edge of the self, holding the line between the inner ground and the outer assault.
Dung and piss: the exhausted waste of the lower nature, the spent leavings of appetite a person is pressed to feed on when reduced to its own refuse.
Rabshakeh: the coarse outer power, the chief cupbearer of the lower self, urging the awakened one to live on its own waste.