Having addressed external, visible afflictions on the skin, the focus now shifts inward to hidden impurities that emerge from within the human body [אבן עזרא, ביאור יש״ר]. This introduces a new system of laws dealing with various secretions from the reproductive system, covering both men and women in natural states and times of illness [פירושי רד צ הופמן].
A fundamental difference exists between these specific secretions and ordinary bodily waste. While the normal expulsion of digestive waste is a necessary, life-sustaining process that does not create impurity, reproductive fluids hold a different status. They are considered the very essence of vitality and the body's most refined nourishment, specifically designed for the creation of new life. When these life-giving materials exit the body without fulfilling their ultimate purpose, they are wasted. They lose their inherent life force, and it is this loss that brings about a state of impurity. In cases of unnatural discharge resulting from illness, the situation involves an internal corruption and weakness of the body's organs. Because this condition can sometimes stem from promiscuous behavior, the resulting impurity is treated with even greater severity [אברבנאל].
God directs these instructions not only to Moses but also to Aaron. The primary approach among commentators is that Aaron and the priests are included because they hold a highly practical role in administering these laws. It is the responsibility of the priests to carefully distinguish between different types of blood to accurately determine a woman's specific state of impurity [אבן עזרא, ביאור יש״ר]. Furthermore, the final purification process from most of these impurities ultimately relies on the service performed by the priest [רלב״ג]. As the instructions continue, they are directed specifically to the Israelites, indicating that the severe laws regarding unnatural discharges apply exclusively to the nation of Israel and do not extend to other nations [מלבי״ם, אילת השחר].