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An impure person is not permitted to enter the Temple or even the Temple Mount before undergoing a purification process as detailed in the Torah. Why not? The reasons for the rules of purity and impurity are divine mysteries beyond our ken and we may never be able to understand fully. Nevertheless, a possible approach, begins with the idea that the Temple represented nothing less than life itself.
It seems purity is connected to life and impurity to death. The more developed the life form, the more severe the loss which comes with death, and thus the greater the accompanying impurity. Therefore, a human corpse is the greatest source of impurity, as humans are the most advanced life form. Lesser impurity can be contracted from animal carcasses or insects. Plants are a less developed life form, so there is no impurity if one comes into contact with a plant that has shriveled and died. However, if one uses plants to grow fruit and vegetables, or to make clothes or vessels, the level of impurity is raised to that below the impurity of dead animals. Another source of impurity is menstruation. It occurs when an egg, which had the potential to develop into a life, exits the woman’s body (together with the blood and uterine lining which were prepared to support the pregnancy). This loss of potential life is why a menstruant is impure. An additional source of impurity is a seminal emission. When a man has a nocturnal emission, it is a waste of sperm, which had the potential to develop into a life. In all these examples, the loss of life or potential life is what creates impurity .
The purification process requires an impure person to submerge his or her entire body in a mikveh. Sometimes this process could be done the day after the person became impure, and other times it could be undergone only a week later. In a case of impurity caused by a human corpse, not only did the person need to wait a week before immersing, one also needed to be sprinkled on the third and seventh days with spring water containing the dissolved ashes of a red heifer. Unfortunately, today we do not have the conditions necessary to practice this ritual.
