SB 5.4.7
brahmanyo ’nyah kuto nabher
vipra mangala-pujitah
yasya barhisi yajñesam
darsayam asur ojasa
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
[The second prayer is this.] “Who is a better worshiper of brahmanas than Maharaja Nabhi? Because he worshiped the qualified brahmanas to their full satisfaction, the brahmanas, by their brahminical prowess, showed Maharaja Nabhi the Supreme Personality of Godhead, Narayana, in person.”
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The brahmanas engaged as priests in the sacrificial ceremony were not ordinary brahmanas. They were so powerful that they could bring forth the Supreme Personality of Godhead by their prayers. Thus Maharaja Nabhi was able to see the Lord face to face. Unless one is a Vaisnava, he cannot call forth the Supreme Personality of Godhead. The Lord does not accept an invitation unless one is a Vaisnava. Therefore it is said in Padma Purana:
sat-karma-nipuno vipro
mantra-tantra-visaradah
avaisnavo gurur na syad
vaisnavah sva-paco guruh
“A scholarly brahmana expert in all subjects of Vedic knowledge is unfit to become a spiritual master without being a Vaisnava, but a person born in a family of a lower caste can become a spiritual master if he is a Vaisnava.” These brahmanas were certainly very expert in chanting the Vedic mantras. They were competent in the performance of the Vedic rituals, and over and above this they were Vaisnavas. Therefore by their spiritual powers they could call on the Supreme Personality of Godhead and enable their disciple, Maharaja Nabhi, to see the Lord face to face. Srila Visvanatha Cakravarti Thakura comments that the word ojasa means “by dint of devotional service.”