On the seventh day the person shaved and washed again in order to prepare for the second offering. Seven days of waiting was a precautionary step to ensure full recovery. The person waited for the ritual to continue on the eighth day in order to be restored to the covenant community. Anthropologists call these ceremonial rituals rites of aggregation.
That is, these are ceremonies in which a person who is in an abnormal social condition is reintegrated into ordinary society.
9 And on the seventh day he shall shave off all his hair from his head, his beard, and his eyebrows. He shall shave off all his hair, and then he shall wash his clothes and bathe his body in water, and he shall be clean.