The word prajā-sarga is very important in this verse. When the saintly King Prācīnabarhi was induced by the great sage Nārada to leave home and take to the devotional service of the Lord, his sons had not yet returned from their austerities in the water. However, he did not wait for their return but simply left messages to the effect that his sons were to protect the mass of citizens. According to Vīrarāghava Ācārya, such protection means organizing the citizens into the specific divisions of the four varṇas and four āśramas. It was the responsibility of the royal order to see that the citizens were following the regulative principles of the four varṇas (namely brāhmaṇa, kṣatriya, vaiśya and śūdra) and the āśramas (namely brahmacarya, gṛhastha, vānaprastha and sannyāsa). It is very difficult to rule citizens in a kingdom without organizing this varṇāśrama-dharma. To rule the mass of citizens in a state and keep them in a complete progressive order is not possible simply by passing laws every year in a legislative assembly. The varṇāśrama-dharma is essential in a good government. One class of men (the brāhmaṇas) must be intelligent and brahminically qualified, another class must be trained in administrative work (kṣatriya), another in mercantile business (vaiśya) and another simply in labor (śūdra). These four classes of men are already there according to nature, but it is the government's duty to see that all four of these classes follow the principles of their varṇas methodically. This is called abhirakṣaṇa, or protection.
It is significant that when Mahārāja Prācīnabarhi was convinced of the goal of life through the instructions of Nārada, he did not wait even a moment to see his sons return, but left immediately. There were many things to be done upon the return of his sons, but he simply left them a message. He knew what his prime duty was. He simply left instructions for his sons and went off for the purpose of spiritual advancement. This is the system of Vedic civilization.
Śrīdhara Svāmī informs us that Kapilāśrama is located at the confluence of the Ganges and the Bay of Bengal, a place known now as Gaṅgā-sāgara. This place is still famous as a place of pilgrimage, and many millions of people gather there every year on the day of Makara-saṅkrānti and take bath. It is called Kapilāśrama because of Lord Kapila's living there to perform His austerities and penances. Lord Kapila propounded the Sāṅkhya system of philosophy.