The introduction established the society and its hierarchical order. According to them we are in the samsara, which is the cycle of life, and based on our karma, which is our behavior (good or bad), we get reborn as something else in the next life. This enabled people to establish hierarchy in the society because it was believed that people who are poor or miserable were made that way by life because they were bad in their previous life. If you were rich and happy that was because you were good in your previous life.