In the course of his meditation, the Treta millennium began, and therefore the principles of the three Vedas, including the process of performing yajna to fulfill fruitive activities, appeared within his heart

Expressions researched:
"In the course of his meditation, the Tretā millennium began, and therefore the principles of the three Vedas, including the process of performing yajña to fulfill fruitive activities, appeared within his heart"

Srimad-Bhagavatam

SB Canto 9

King Purūravā then left Agnisthālī in the forest and returned home, where he meditated all night upon Urvaśī. In the course of his meditation, the Tretā millennium began, and therefore the principles of the three Vedas, including the process of performing yajña to fulfill fruitive activities, appeared within his heart.

SB 9.14.43, Translation and Purport

King Purūravā then left Agnisthālī in the forest and returned home, where he meditated all night upon Urvaśī. In the course of his meditation, the Tretā millennium began, and therefore the principles of the three Vedas, including the process of performing yajña to fulfill fruitive activities, appeared within his heart.

It is said, tretāyāṁ yajato makhaiḥ: in Tretā-yuga, if one performed yajñas, he would get the results of those yajñas. By performing viṣṇu-yajña specifically, one could even achieve the lotus feet of the Supreme Personality of Godhead. Of course, yajña is intended to please the Supreme Personality of Godhead. While Purūravā was meditating upon Urvaśī, the Tretā-yuga began, and therefore the Vedic yajñas were revealed in his heart. But Purūravā was a materialistic man, especially interested in enjoying the senses. Yajñas for enjoyment of the senses are called karma-kāṇḍīya-yajñas. Therefore, he decided to perform karma-kāṇḍīya-yajñas to fulfill his lusty desires. In other words, karma-kāṇḍīya-yajñas are meant for sensuous persons, whereas yajña should actually be performed to please the Supreme Personality of Godhead. To please the Supreme Personality of Godhead in Kali-yuga, the saṅkīrtana-yajña is recommended. Yajñaiḥ saṅkīrtana-prāyair yajanti hi sumedhasaḥ (SB 11.5.32). Only those who are very intelligent take to saṅkīrtana-yajña to fulfill all their desires, material and spiritual, whereas those who are lusty for sense enjoyment perform karma-kāṇḍīya-yajñas.