The Demigods Are The Supreme Lord’s Powerful Representatives by His Divine Grace A.C.Bhaktivedanta Swami Prabhupada.
Lord Vishnu is even the Supreme Lord of death, as confirmed in Bhagavad-gītā (mṛtyuḥ sarva-haraś cāham [Bg. 10.34]). The two kinds of activity—auspicious and inauspicious— are both controlled by Lord Vishnu. Inauspicious activities are said to be behind Lord Vishnu, whereas auspicious activities stand before Him. The auspicious and the inauspicious exist throughout the entire world, and Lord Vishnu is the controller of both.
Srila Madhvacarya says:
sthitaṁ harim upāsate
In all the various lands, fields, mountains and oceans found throughout the creation, the Supreme Personality of Godhead is worshiped by His different names.
Srila Viraraghava Acarya explains: The original cause of the cosmic manifestation must be the oldest person and must therefore be beyond material transformations. He is the enjoyer of all auspicious activities and is the cause of both conditional life and liberation. The demigod Surya, who is categorized as a very powerful jiva, (living entity), is a representation of one of the parts of His body. Human beings are naturally subordinate to powerful living entities, and therefore we can worship the various demigods as the powerful representatives of the Supreme Personality of Godhead. The sun-god is worshiped not as the Supreme Personality of Godhead Himself, but as His powerful representative.
In the Kaṭha Upaniṣad (1.3.1) it is said:
ṛtaṁ pibantau sukṛtasya loke
guhāṁ praviṣṭau parame parārdhe
chāyātapau brahmavido vadanti
pañcāgnayo ye ca tri-ṇāciketāḥ
“O Naciketa, the dual expansions of Lord Vishnu – as the tiny living entity and the Supersoul – are both situated within the cave-like heart of this body. Having entered that cavity, the living entity, resting on the chief of the life airs, enjoys the results of activities, and the Supersoul, acting as witness, enables him to enjoy them. Those who are well-versed in knowledge of Brahman and the householders who carefully follow the Vedic regulations say that the difference between the two is like the difference between a shadow and the sun.”
In the Śvetāśvatara Upaniṣad (6.16) it is said:
sa viśvakṛd viśvavidātmayoniḥ
jñaḥ kālākāro guṇī sarvavid yaḥ
The Supreme Lord, the creator of this cosmic manifestation, knows every nook and cranny of His creation. Although He is the cause of creation, there is no cause for His appearance. He is fully aware of everything. He is the Supersoul, the master of all transcendental qualities, and He is the master of this cosmic manifestation in regard to bondage to the conditional state of material existence and liberation from that bondage.”
Similarly, in the Taittirīya Upaniṣad (2.8) it is said:
bhīṣāsmād vātaḥ pavate
bhīṣāsmād agniś candraś ca
mṛtyur dhāvati pañcamaḥ
“It is out of fear of the Supreme Brahman that the wind is blowing; out of fear of Him the sun regularly rises and sets, and out of fear of Him fire burns. It is only due to fear of Him that death and Indra, the King of heaven, perform their respective duties.”
As described in this chapter, the inhabitants of the five islands beginning with Plaksadvipa worship the sun-god, the moon-god, the firegod, the air-god and Lord Brahma respectively. Although they engage in the worship of these five demigods, however, they actually worship Lord Vishnu, the Supersoul of all living entities, as indicated in this verse by the words pratnasya viṣṇo rūpam. Vishnu is brahma, amṛta, mṛtyu—the Supreme Brahman and the origin of everything, auspicious and inauspicious. He is situated in the heart of everyone, including all the demigods.
As stated in Bhagavad-gītā (7.20), kāmais tais tair hṛta-jñānāḥ prapadyante ‘nya devatāḥ: “Those whose minds are distorted by material desires surrender unto the demigods.” People who are almost blind because of lusty desires are recommended to worship the demigods to have their material desires fulfilled. However in actuality their desires are not fulfilled by the material demigods for whatever the demigods do is done with the sanction of Lord Vishnu. People who are avaricious worship various demigods instead of worshiping Lord Vishnu, the Supersoul of all living entities. However, it is ultimately Lord Vishnu they worship because He is the Supersoul of all demigods.
— Śrīmad-Bhāgavatam » Canto 5 » Chapter 20: Studying the Structure of the Universe » Verse: 5, Purport.