vacanāt - by the order or the words; deva-devasya - of the Supreme Lord of all demigods; viṣṇoḥ - Lord Viṣṇu; viśva-ātmanaḥ - the Supersoul of the entire creation; prabhoḥ - the Lord, the controller; vāhanatve - because of becoming the carrier; vṛtaḥ - engaged; tasya - in the service of Purañjaya; babhūva - he became; indraḥ - the King of heaven; mahā-vṛṣaḥ - a great bull.

Purañjaya agreed to kill all the demons, on the condition that Indra would be his carrier. Because of pride, Indra could not accept this proposal, but later, by the order of the Supreme Lord, Viṣṇu, Indra did accept it and became a great bull carrier for Purañjaya.