וְאֶל־אִשָּׁה בְּנִדַּת טֻמְאָתָהּ לֹא תִקְרַב
And to a woman during the uncleanness of her separation, you shall not come near.
Shir Hashirim Rabbah illustrates the meaning of the verse in Song of Songs (7:3), “Thy belly is like a heap of wheat set about with lilies,” in this way:
It often happens that a man takes a wife when he is forty years of age. When, after going to great expense, he wishes to associate with her, she says to him, “I have seen a rose-red speck,” he immediately recoils. What made him retreat and keep away from her? Was there an iron fence, did a serpent bite him, did a scorpion sting him? A dish of meat is placed before a man and he is told some forbidden fat has fallen into it. He withdraws his hand from the food. What stopped him from tasting it? Did a serpent bite him; did a scorpion sting him? Only the words of the Torah which are as soft as a bed of lilies.
Bride and bridegroom are young, physically strong and passionately in love with each other. Both have patiently waited for this rendezvous to take place. Just one more step and their love would have been fulfilled, a vision realized. Suddenly the bride and groom make a movement of recoil. He, gallantly, like a chivalrous knight, exhibits paradoxical heroism. He takes his own defeat. There is no glamor attached to his withdrawal. The latter is not a spectacular gesture, since there are no witnesses to admire and to laud him. The heroic act did not take place in the presence of jubilant crowds; no bards will sing of these two modest, humble young people. It happened in the sheltered privacy of their home, in the stillness of the night. The young man, like Jacob of old in his encounter with the angel, makes an about-face; he retreats at the moment when fulfillment seems assured.
The idea of catharsis through the dialectical movement manifests itself in all Halachic norms regulating human life. Nowhere, however, does this doctrine of dialectical catharsis assert itself more frequently than it does in the aesthetic-hedonic realm. How does man purge himself in this realm? By engaging in the dialectical movement: by withdrawing, at the moment when passion reaches its peak. The stronger the grip of the physiological drive is felt by man, the more intoxicating and bewildering the prospect of hedonic gratification, the greater the redemptive capacity of the dialectical catharsis – the movement of recoil. (Catharsis, p. 45-46)