It is written in the Srimad Bhagavatam 11/5/41: Whoever completely renounces all material relationships and seeks absolute refuge at the lotus feet of the Lord, who gives us liberation and is alone worthy to become our refuge, is no longer indebted to anyone, nor does he have to serve anyone, whether they are demigods, ancestors, sages, relatives, other members of society, or anyone else.
Therefore, there was nothing reprehensible in the Kumaras' reaction when they opposed the request of their illustrious father, who wished them to become householders.
Brahma said: Sanaka, Sanatana, Sanandana, and Sanat-kumara, all four born of my mind, came into being before you. They sometimes travel the material and spiritual worlds without any specific aspiration.
These four saints harbor no material desires, yet they sometimes travel spontaneously across the entire galaxy to preach devotional service.
One day, after thus traveling all the galaxies, they entered the spiritual world, since they were free from all material defilement. This world houses spiritual planets called Vaikunthas, which serve as the abode of the Supreme Lord and His pure devotees, and are worshipped by the inhabitants of all material planets.
The Four Kumara Brothers, Avatars of Knowledge.
The Lord, pleased with the austerities Brahma had performed to create the various planetary systems of the galaxy, manifested Himself in the persons of the four Kumara brothers: Sanaka, Sanat-kumara, Sanandana, and Sanatana.
Absolute knowledge had been lost in the devastation of the previous creation, but the four Kumara brothers explained it with such clarity that the sages were able to immediately assimilate it.
Living beings are qualitatively identical to the Lord in their eternal nature, but He is the Supreme and Absolute Eternal, unlike the separate beings, minute parts of Him, who can eventually fall into the atmosphere of non-eternity. Therefore, from a quantitative point of view, the separate beings differ from Krishna, the Supreme and Absolute Eternal Lord.
Brahma desired to create the entire cosmic manifestation as it was in the previous era, and since knowledge of the Absolute had completely disappeared from the universe in the last apocalypse, he wished to see this same knowledge revived, otherwise creation would have no purpose.
Spiritual and absolute knowledge is of primary necessity for souls eternally conditioned by matter, who are thus offered an opportunity to achieve liberation during each cosmic cycle.