PURPORT

King Indra wondered how Vrtrasura could have been elevated to the position of an exalted devotee. As for Prahlada Maharaja, he was initiated by Narada Muni, and therefore it was possible for him to become a great devotee, although he was born in a family of demons. For Vrtrasura, however, Indra could not detect such causes. Therefore he was struck with wonder that Vrtrasura was such an exalted devotee that he could fix his mind without deviation upon the lotus feet of Lord Krsna, Vasudeva.