What is the purpose of the waiting period ('Iddah)?

Primary text

The purpose of the waiting period is not solely the preservation of lineage. If it were solely for lineage, it would not be obligatory upon the woman who undergoes *Mula'anah* (mutual imprecation, after which the child's lineage is negated), the one who has reached menopause (Al-A'isah), or the young girl. Likewise, it would not be obligatory upon a female slave whose child's lineage is not attributed to her seller. If lineage preservation were the sole reason, the waiting period should be required on the seller of the female slave.