Why does the Torah outline many different degrees of impurity טומאה with different purification methods?
You have corpse-impurity which requires sprinkling with the water of the red heifer during a seven-day waiting period. Beyond that, there are multiple levels of impurity which require possibly waiting some amount of time and then immersion in a mikveh (or immersion in the mikveh and then waiting some amount of time) for purification.
Why is there a need for all of these different types of ritual impurity and purification methods? What is the difference between them that causes them to be treated differently?