Mahabharata 3.149.26

3.149.26

na hi dharmamavijñāya vṛddhānanupasevya ca |
dharmo vai vedituṃ śakyo bṛhaspatisamairapi || 26 ||

Without knowing duties and serving the old, even persons like unto Vrihaspati cannot understand profit and religion. One should ascertain with discrimination those cases in which vice goeth under the name of virtue, and virtue goeth under the name of vice,--(cases) in which people destitute of intelligence become perplexed. From religious observances proceedeth merit; and in merit are established the Vedas; and from the Vedas sacrifices come into existence; and by sacrifices are established the gods. The gods are maintained by the (celebration of) sacrifices prescribed by the Vedas and the religious ordinances; while men maintain themselves by (following) the ordinances of Vrihaspati and Usanas and also by these avocations, by which the world is maintained,--serving for wages, (receiving) taxes, merchandise, agriculture and tending kine and sheep. The world subsisteth by profession. The (study of the) three Vedas and agriculture and trade and government constitutes, it is ordained by the wise, the professions of the twice born ones; and each order maintaineth itself by following the profession prescribed for it. And when these callings are properly pursued, the world is maintained with ease. If, however, people do not righteously lead their lives, the world becometh lawless, in consequence of the want of Vedic merit and government.