N hinduism the system of four "stations" of life (a social stratification) that includes priestly, warrior, merchant and servant categories is call what?

The answer is Caste System. This social stratification is very important to many Hindus. They believed that they will go through all of these stages in life if they have done well in their current one. It is their form of social order as well as it dictates the social role of each caste.