The constant struggle[1]
ואל אשה בנדת טומאתה לא תקרב וגו’
Do not approach a woman in her impure state of niddah[2]
The gemarra relates[3] a conversation between a Sadducee[4], someone who rejected Rabbinic Judaism, and the Sages of his time. He asked Rav Kahana, how could a man and woman be trusted to be alone together when the wife is a niddah[5]? Once she has her period, she and her husband are forbidden to each other until she immerses in a mikveh at the right time. He asked is it possible for a fire to kindle and not burn?