Rav Yehuda Henkin, Halachic Authority for Nishmat
Why is the yoledet temeah?

Rabbi Dr. Norman Lamm, “A Hedge of Roses”

Unrestricted approachability leads to over-indulgence. And this over-familiarity, with its consequent satiety and boredom and ennui, is a direct and powerful cause of marital disharmony. When, however, the couple follows the Torah‘s sexual discipline and observes this period of separation, the ugly spectre of over-fulfillment and habituation is banished and the refreshing zest of early love is ever-present.

There is so much insight in this comment of the rabbis! Familiarity does indeed breed contempt, and a little absence does make the heart grow fonder…

Yoetzet Halacha Dr.  Deena Zimmerman MD MPH

“So She Can Be as Dear to Him as on Their Wedding Day”? Modern Concerns with Hilkhot Niddah as Demonstrated by Anonymous Email Questions

Rabbi Joseph B. Soloveitchik, Family Redeemed, p. 50

The very intimate sex relationship of husband and wife is disciplined by Halakha. Strict laws of separation have been formulated which drastically reduce the sexual activity of the couple and the Halakhah is persistent in its demand for full implementation of those restrictive laws. For only withdrawal and self-discipline purge and redeem the primitive and vulgar sex drive–a biological pressure which is common to man and beast.

Rabbi Aharon Lichtenstein, “Of Marriage- Relationship and Relations” Tradition 39:2

It is precisely in order to underscore the significance of sexual relations, in order to focus attention upon their character and consequences, that tevila was ordained. The restraints imposed sans tevila are intended to assure that relations not be casual. They generate interactive awareness which serves to ennoble and enhance sexuality, elevating it, redemptively, from the bestial to the human.

Rabbi Saul Berman, “Coming to Grips with Awe”

The purpose of temporary withdrawal in the Torah was in fact the affirmation of the significance of the activity as an essential human endeavor which, however, requires periodic withdrawal for the purpose of evaluation… The withdrawal from the sexual relationship between husband and wife for some days of every menstrual cycle is not a negation of the significance of that dimension of the spousal relationship. On the contrary, it is an affirmation of its significance and a call to think about the goals of intimacy and mutuality, of commitment and interdependence – and whether they are being adequately achieved within the context of that marital relationship.