Question:
I've read that one of the reasons behind the mitzvah of Family Purity is to prevent apathy from creeping into a marriage—the monthly period of separation constantly infusing renewed passion into the relationship. But what happens when a woman goes into menopause, is apathy okay at that point?
Answer:
Thank you for your inquiry. The one and only reason behind the mitzvah of taharat hamishpachah (Family Purity) is that G‑d said so. He gave us no explanation; like other chukim (mitzvot with no obvious rationale), we observe these laws because G‑d commanded them. Indeed, as we are involved in the observance of mitzvot, we find significance—sometimes commonly experienced, and sometimes just personally—and that is why you read that one of the meaningful experiences for couples is the reality that absence does, indeed, often make the heart grow fonder.
Apathy isn't healthy in any important area of life, and certainly not in the relationship between husband and wife. For most couples, during the expanses of time when a woman and her husband need to be aware of their permitted or prohibited intimate interactions, they are training their psyches to be sensitive towards each other, to know the feeling of longing and desire. Self-discipline is exquisitely honed.
For many couples well into menopause, the “training” of the years of cyclical abstinence and reunion leaves them with a relationship that's richer for having created and nurtured all manner of personal, emotional interaction. Like any other exercise, when a couple reaches menopause they have had developed all the different ways they experience intimacy. These various languages of intimacy don't disappear when abstinence is no longer a regular expectation.
To reiterate, the laws are observed solely for reasons we don't know. Observance of these laws creates a marriage that is holy. However, absent menstruation, a couple's marriage is no less holy; these laws are contingent on a specific circumstance: menstruation.
Whether a couple is more often pregnant than not, whether a couple is on medication that prevents menstruation, whether a couple is post-menopause no matter the age of the woman, the laws of taharat hamishpachah—observed as often as the circumstances dictate—are the very foundation of a Jewish marriage.
Bronya Shaffer for Chabad.org
The Rabbis teach: Why were the laws of nida given? "Kiday l'chavev isha al baala", in order to make a woman more precious to her husband, as precious, they say, like on the day of the Chupa, the day they stood under the Chupa together.
Hashem created a man to always desire what's out of his reach. With the laws of Nida, his own wife is the "unattainable" for 2 weeks out of every month for many years.
If any Torah laws can show so clearly that the same One who created the world, created the Torah, it's these beautiful laws.
And when a woman goes to the mikva, it's like she's reborn in the waters, like emerging from her mother's womb. There's an amazing book by Aryeh Kaplan called Waters of Eden that explains this and much more.