If a man remarries a woman from whom he had irrevocably separated while she is still observing her waiting period, then divorces her before consummating the marriage, she completes her former waiting period.
His statement, “If a man remarries a woman from whom he had irrevocably separated while she is still observing her waiting period, then divorces her before consummating the marriage, she completes her former waiting period”: irrevocable separation occurs in three cases: annulment, divorce in exchange for compensation, and a divorce that completes the prescribed number of divorces. The forms of irrevocable separation possible here are divorce in exchange for compensation and annulment. As for a divorce that completes the prescribed number, this is not possible, because she is not lawful for him until she has married another husband.
Thus, a man divorces his wife in exchange for compensation, and she becomes irrevocably separated from him. Yet he wishes to take her back. We say: she is not lawful for you except through a new marriage contract. So he contracts marriage with her, while she is still observing her waiting period, but then divorces her before consummating the marriage. The author says: she completes her original waiting period. Thus, if she had menstruated twice and he married her, but then divorced her before having intercourse with her, we say: one menstrual cycle remains, which she completes, and then her waiting period ends. The new marriage contract does not require a new waiting period, because its cause has not occurred: one of the conditions for a waiting period is that intercourse or seclusion take place, whereas here neither intercourse nor seclusion occurred.
A second example: a woman whose husband discovers a defect in her and annuls the marriage because of that defect. Then, after annulling the marriage, he reconsiders and marries her while she is still observing her waiting period. If he then divorces her before having intercourse with her, she completes her original waiting period, because no cause for a new waiting period has occurred.
But if the divorce was revocable—for example, a man divorces his wife with a revocable divorce, then takes her back, and subsequently divorces her before consummating the marriage—does she complete her prior waiting period, or begin a new one?
The answer is that she begins a new waiting period, observing three menstrual cycles apart from the first, because when he took her back, he restored her to the original marriage, and taking her back is not a new marriage contract.