People, they are interested for success of this human form of life. They are called brahmin. And the next class of men, they are interested for political power, next important class. First important class men is called who are seeking success of the human form of life, and the next class, they are seeking success to become very rich within this material world by political power. Another, next class, is trying to be successful by material opulence, by earning money, the mercantile community. First class, second class, third class. They are third class.
And the fourth-class men, they are called śūdras. That means they have no other ambition than to fill up their belly only. That's all. They have no intelligence to become brahmin, neither to become kṣatriya, administrator, or to occupy political powers; neither they have energy to become very rich businessmen or industrialists. Therefore they are called fourth-class men.