The man clothed in linen is the purified will, sent down through the turning wheels of the body's own powers to reach the fire beneath its highest station. The coals gathered from between the cherubims are living heat drawn from the seat of spirit within, and scattering them over the city is the release of that fire through the crowded mass of ordinary thought and habit.
The descent happens inside, not over stone streets. The purified part goes down into the machinery of the flesh, takes up the divine fire stored at the center, and lets it fall through the whole population of the mind, so what is dead burns away and only what can bear the heat remains.
Man clothed with linen: the purified will in a person, wrapped in cleanness and sent to do the inner work
Wheels: the turning powers and cycles of the body through which the will must pass
Cherub: the guarding intelligence of spirit seated above the body's forces
Coals of fire: the living divine heat stored at the center of a person, gathered to be released
City: the crowded mass of thoughts and habits a person carries, given over to the fire