Refers to the great wisdom of Purusha-a God figure. All things are a part of him. In Vedic thought, the entire universe was born of a sacrifice, and furthermore the universe was maintained by proper sacrifice. It was man's responsibility to maintain order by properly performing ritual duty. Compare to Egyptian concept of ma'at.
Brahman refers to the priestly caste, who spoke spells and performed rituals.
Rajanya refers to the royalty, or kshatriya, warriors who maintained civil order and fought enemies. Vaisya refers to the worker caste, merchants, craftsmen, farmers, etc. The producers of society. Sudra refers to the slave caste, most likely the darker, indigenous people of India conquered by Indo-Aryan invaders. The Sudra who performed hard labor and served other castes.