Princess Razal
From http://www.mikvah.org/article/the_three_mitzvot_of_the_woman
As a woman, the potential giver of life, you hold the power to elevate your home and family from the physically mundane to the spiritually sublime. The adherence to the Laws of Family Sanctity and Mikvah give you the opportunity
to invite G-d into the most intimate area of your life, bringing G-dliness to every aspect of your lives and impacting the soul of any child conceived. Your observance brings holiness and blessing, not only to your most physical self, but sanctifies your entire family and your entire home. Immersion in the mikvah is a Biblical commandment of the highest ordinance.
The Jewish marriage sanctifies husband and wife. Taharat Hamishpacha (Family Sanctity) observance introduces times of intimate separation and reunion as part of a cycle in married life. Separation begins with the onset of the menstrual flow. It is a time when the depth of the husband-wife relationship is expressed without physical intimacy. It is a period of anticipation and preparation for mikvah immersion. The reunion which follows holds the highest potentialfor sanctity in marriage.