Srimad Bhagavatham : -5.4.7 :




[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.” 

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 Vaishnava, he cannot call forth the Supreme Personality of Godhead. The Lord does not accept an invitation unless one is a Vaishnava. Therefore it is said in Padma Puranam :