Why does the 'iddah of a woman who has not yet menstruated differ from the 'iddah of a woman divorced before consummation?

The young woman who has not menstruated, her 'iddah (waiting period) is three months, based on the Almighty's saying: ﴿And those women who have passed the age of menstruation among your women – if you have doubts, their waiting period is three months, and also those who have not menstruated.﴾ There is no objection to the husband having intercourse with his young wife if she is capable of it, even if she has not menstruated.

If the husband has intercourse with his young wife, she must observe the 'iddah to confirm the absence of pregnancy, as the absence of menstruation does not mean the absence of pregnancy. However, if he secluded himself with her but did not have intercourse, there is a difference of opinion among scholars regarding the necessity of 'iddah for her, and the preponderant view is that it is obligatory, based on the consensus of the Companions.

The 'iddah has other wisdoms besides confirming pregnancy, including providing an opportunity for reconciliation between the spouses. This is why the 'iddah period was made longer, and the wife was commanded to remain in the marital home, as her staying near her husband helps in reconciliation, unlike the woman who seeks khul' (divorce initiated by the wife), whose 'iddah is one menstrual cycle, because the husband does not have the right to take her back after khul' except with a new contract.