SB 6.7.39

The distinction between the demigods ( devas ) and demons ( asuras ) is that the demigods are all devotees of Lord Viṣṇu whereas the demons are devotees of demigods like Lord Śiva, Goddess Kālī and Goddess Durgā. Sometimes the demons are also devotees of Lord Brahmā. For example, Hiraṇyakaśipu was a devotee of Lord Brahmā, Rāvaṇa was a devotee of Lord Śiva, and Mahiṣāsura was a devotee of Goddess Durgā. The demigods are devotees of Lord Viṣṇu ( viṣṇu-bhaktaḥ smṛto daiva ), whereas the demons ( āsuras tad-viparyayaḥ ) are always against the viṣṇu-bhaktas, or Vaiṣṇavas. To oppose the Vaiṣṇavas, the demons become devotees of Lord Śiva, Lord Brahmā, Kālī, Durgā, and so on. In the days of yore, many long years ago, there was animosity between the devas and the asuras, and the same spirit still continues, for the devotees of Lord Śiva and Goddess Durgā are always envious of Vaiṣṇavas, who are devotees of Lord Viṣṇu. This strain between the devotees of Lord Śiva and Lord Viṣṇu has always existed. In the higher planetary systems, fights between the demons and the demigods continue for a long, long time.

Herein we see that Viśvarūpa made for the demigods a protective covering, saturated with a Viṣṇu mantra. Sometimes the Viṣṇu mantra is called Viṣṇu-jvara, and the Śiva mantra is called Śiva-jvara. We find in the śāstras that sometimes the Śiva-jvara and Viṣṇu-jvara are employed in the fights between the demons and the demigods.

The word sura-dviṣām, which in this verse means “of the enemies of the demigods,” also refers to the atheists. Śrīmad-Bhāgavatam elsewhere says that Lord Buddha appeared for the purpose of bewildering the demons or atheists. The Supreme Personality of Godhead always awards His benediction to devotees. The Lord Himself confirms this in Bhagavad-gītā (9.31) :

kaunteya pratijānīhi na me bhaktaḥ praṇaśyati

“O son of Kuntī, declare it boldly that My devotee never perishes.”