Leaven is the swelling of the ego, the puffing agent that inflates the bread of the self with pride and old corruption, and putting it out of the houses is clearing it from the chambers of the body. The number 7 is the full span of completion, the whole cycle of purification through which the flat, unpuffed self must be eaten, day after day, until the passage is finished. The house is the body, and every room of it must be swept of the rising influence before the higher state can pass over.
What swells the sense of self with vanity is the very thing that severs a person from the ordered inner kingdom, so the work is to keep the self flat and clean through the whole cycle.
Unleavened bread: the flat, unpuffed self, consciousness kept clear of pride and the old swelling of ego
Leaven: the puffing agent of vanity and corruption that inflates the ego and rots the inner bread
7 days: the complete cycle of purification, the full span in which the self is cleansed of its swelling
Houses: the chambers of the body that must be swept clean of the ego's rising influence