For seven days beforehand, the High Priest prepared. The entire night before Yom Kippur, he was tested by a group of great Jewish leaders, who pushed him to the heights of his moral and spiritual potential. The future of the Jewish Nation and the entire world would rest on his encounter alone with G-d the next day. Resumption of the intimacy between husband and wife is similarly awesome. After seven days of preparing for this moment, a woman immerses in order to elevate her relationship with her husband and to elevate the world itself.
Water is said to be the most spiritual of all elements.
The water in a mikvah is the closest we have to a piece of this Divine essence on earth. Its waters are untouched by human hands, having been collected from rainfall or from an underground source. When a woman visits the mikvah, just prior to immersing herself in these G-dly waters, she utters a prayer asking the Almighty to join her in the sacred act of conjugal union. Upon immersing she, in a sense, touches hands with the Creator of the world. In a sense, a woman creates her family.