Rambam - Sefer HaMitzvos: Positive Mitzvah 108, 101: Positive Mitzvah 108, 101

Positive Mitzvah 108: The Purifying Water
Numbers 19:21 "And he that touches the water of sprinkling (purification water), shall be unclean"

A person purifying himself after contact with a dead body must follow certain procedures. One step of his purification process involves Niddah Water.

This is a mixture of natural spring water, combined with the ashes of the Parah Adumah - the red heifer (cow). (See Positive Mitzvah 113).

This water possesses special qualities and when used properly, it can purify. However, it could cause the opposite effect on a person who touches the water for other purposes.

Imagine yourself sitting around a bonfire, enjoying the warmth, pleasant glow and atmosphere. Those same flames which cause so much pleasure, can also burn and destroy if one is careless.

Similarly, this purifying water can cause a person who misuses them to become impure.

Positive Mitzvah 101: Impurity of a Metzorah
Leviticus 13:2 "When a man shall have on the skin of his flesh..."

A person whose body has the signs of the Tzara'at affliction (see Positive Mitzvah 77), is considered impure. These signs appear as a skin ailment, but Tzara'at is not a physical disease treated by a doctor. Rather, it is the priest, who is dedicated to the service of HaShem, that determines the impurity of these signs. Through his guidance and care, the afflicted person can purify himself.

The priest will help the person with Tzara'at to correct his deeds and remove the cause of his affliction.

The essential teaching of the Baal Shem Tov:
Be simple, be earnest, and spread that simplicity throughout everything you do. Simplicity is a receptacle for G-d's simple oneness.

From: Bringing Heaven Down to Earth by Tzvi Freeman - tzvif@aol.com