yaviyamsa ekasitir jayanteyah pitur adesakara maha-salina maha-srotriya yajña-silah karma-visuddha brahmana babhuvuh.
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
In addition to these nineteen sons mentioned above, there were eighty-one younger ones, all born of Rsabhadeva and Jayanti. According to the order of their father, they became well-cultured, well-behaved, very pure in their activities and expert in Vedic knowledge and the performance of Vedic rituals. Thus they all became perfectly qualified brahmanas.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
From this verse we have good information of how the castes are qualified according to quality and work. Rsabhadeva, a king, was certainly a ksatriya. He had a hundred sons, and out of these, ten were engaged as ksatriyas and ruled the planet. Nine sons became good preachers of Srimad-Bhagavatam (maha-bhagavatas), and this indicates that they were above the position of brahmanas. The other eighty-one sons became highly qualified brahmanas. These are some practical examples of how one can become fit for a certain type of activity by qualification, not by birth. All the sons of Maharaja Rsabhadeva were ksatriyas by birth, but by quality some of them became ksatriyas, and some became brahmanas. Nine became preachers of Srimad-Bhagavatam (bhagavata-dharma-darsanah), which means that they were above the categories of ksatriya and brahmana.