Adiyen Ramanuja Dasan
Adiyen will try to answer swami from srimad bhagavatham swami
After Viśvarūpa was killed, his father, Tvaṣṭā, performed a sacrifice to kill Indra. Unfortunately, if mantras are chanted irregularly, they yield an opposite result. This happened when Tvaṣṭā performed this yajña. While performing the sacrifice to kill Indra. Tvaṣṭā chanted a mantra to increase Indra’s enemies, but because he chanted the mantra wrong, the sacrifice produced an asura named Vṛtrāsura, of whom Indra was the enemy.
Vritasura still had material bonding and wanted to take revenge on Indra for killing his brother viswaroopa however he prays paramatma to renounce his bondings still did his purpose.
King Indra had first accepted Viśvarūpa as his priest and thereafter killed him. Reminding Indra of his heinous activities, Vṛtrāsura said, “If one is a devotee of the Supreme Personality of Godhead, Lord Viṣṇu, and depends on Lord Viṣṇu in every respect, then victory, opulence and peace of mind are all inevitably available. Such a person has nothing for which to aspire in the three worlds. The Supreme Lord is so kind that He especially favors such a devotee by not giving him opulence that will hamper his devotional service. Therefore I wish to give up everything for the service of the Lord. I wish always to chant the glories of the Lord and engage in His service. Let me become unattached to my worldly family and make friendships with the devotees of the Lord. I do not desire to be promoted to the higher planetary systems, even to Dhruvaloka or Brahmaloka, nor do I desire an unconquerable position within this material world. I have no need for such things.” this shows Vritasuras greatness as sri vaishnava , karma is karma Indra has to face it but with namperumals extreme grace and indras acceptance of his sin and surrender to sri hari.
Indra admitted himself that vritasura was greatest devotee even though he is a demon but both understand the war as kainkaryam as per bhagavatam
iti bruvāṇāv anyonyaṁ
dharma-jijñāsayā nṛpa
yuyudhāte mahā-vīryāv
indra-vṛtrau yudhām patī
Vṛtrāsura and King Indra spoke about devotional service even on the battlefield, and then as a matter of duty they again began fighting.
After this Indra and his elephant was swallowed
By Vritasura and he thought indra was dead then vritasura was ready to leave his body by yoga samadhi when vritasura body was immobile then indra being protected tore open his abdomen and cut head for 360 days after actual vritasura jeevathma already attained moksha.
When all the devas requested Indra to kill Vṛtrāsura since asura army led by vritasura were killing devas already, he refused because Vṛtrāsura was a brāhmaṇa but Indra fought Vṛtrāsura, but when Vṛtrāsura was killed, everyone was satisfied but Indra, who knew Vṛtrāsura’s position. This is the nature of a great personality. Even if a great personality acquires some opulence, he is always ashamed and regretful if he acquires it illegally. Indra could understand that he was certainly entangled by sinful reactions for killing a brāhmaṇa. Indeed, he could see sinful reaction personified following him, and thus he fled here and there in fear, thinking of how to rid himself of his sins.
We can easily misunderstand anything swamy