yad rajaḥ-prakṛtes tava
sattvātmani dṛḍhā matiḥ
King Indra wondered how Vṛtrāsura could have been elevated to the position of an exalted devotee. As for Prahlāda Mahārāja, he was initiated by Nārada Muni, and therefore it was possible for him to become a great devotee, although he was born in a family of demons. For Vṛtrāsura, however, Indra could not detect such causes. Therefore he was struck with wonder that Vṛtrāsura was such an exalted devotee that he could fix his mind without deviation upon the lotus feet of Lord Kṛṣṇa, Vāsudeva.