yo yo yāḿ yāḿ tanuḿ bhaktaḥ
śraddhayārcitum icchati
tasya tasyācalāḿ śraddhāḿ
tām eva vidadhāmy aham

Translation of Bhagavad Gita 7.21

I am in everyone’s heart as the Supersoul. As soon as one desires to worship some demigod, I make his faith steady so that he can devote himself to that particular deity.

Commentary by Sri A.C. Bhaktivedanta Swami Prabhupada of Gaudiya Sampradaya:

God has given independence to everyone; therefore, if a person desires to have material enjoyment and wants very sincerely to have such facilities from the material demigods, the Supreme Lord, as Supersoul in everyone’s heart, understands and gives facilities to such persons. As the supreme father of all living entities, He does not interfere with their independence, but gives all facilities so that they can fulfill their material desires. Some may ask why the all-powerful God gives facilities to the living entities for enjoying this material world and so lets them fall into the trap of the illusory energy. The answer is that if the Supreme Lord as Supersoul does not give such facilities, then there is no meaning to independence. Therefore He gives everyone full independence—whatever one likes—but His ultimate instruction we find in the Bhagavad-gita: one should give up all other engagements and fully surrender unto Him. That will make man happy.

Both the living entity and the demigods are subordinate to the will of the Supreme Personality of Godhead; therefore the living entity cannot worship the demigod by his own desire, nor can the demigod bestow any benediction without the supreme will. As it is said, not a blade of grass moves without the will of the Supreme Personality of Godhead. Generally, persons who are distressed in the material world go to the demigods, as they are advised in the Vedic literature. A person wanting some particular thing may worship such and such a demigod. For example, a diseased person is recommended to worship the sun-god; a person wanting education may worship the goddess of learning, Sarasvati; and a person wanting a beautiful wife may worship the goddess Uma, the wife of Lord Shiva. In this way there are recommendations in the shastras (Vedic scriptures) for different modes of worship of different demigods. And because a particular living entity wants to enjoy a particular material facility, the Lord inspires him with a strong desire to achieve that benediction from that particular demigod, and so he successfully receives the benediction. The particular mode of the devotional attitude of the living entity toward a particular type of demigod is also arranged by the Supreme Lord. The demigods cannot infuse the living entities with such an affinity, but because He is the Supreme Lord, or the Supersoul who is present in the hearts of all living entities, Krishna gives impetus to man to worship certain demigods. The demigods are actually different parts of the universal body of the Supreme Lord; therefore they have no independence. In the Vedic literature it is stated: “The Supreme Personality of Godhead as Supersoul is also present within the heart of the demigod; therefore He arranges through the demigod to fulfill the desire of the living entity. But both the demigod and the living entity are dependent on the supreme will. They are not independent.”

Commentary by Sri Vishvanatha Chakravarthi Thakur of Gaudiya Sampradaya:

You should not say that the devata, pleased with being worshiped, will produce faith in worshipping the Supreme Lord, in order to give benefit of their worshippers. As those devatas cannot even produce faith in those people to worship the devatas, how then can they produce faith to worship me? When those people desire to worship forms (tanum) such as Surya, which are actually my forms since they are my vibhutis, I, as paramatma, give the faith in those forms of devatas. The devatas do not give the faith.

Commentary by Sri Ramanuja of Sri Sampradaya:

7.21 These divinities too constitute My body as taught in the Sruti text like: ‘He who, dwelling in the sun, whom the sun does not know, whose body is the sun’ (Br. U., 3.7.9). Whichever devotee seeks to worship with faith whatever form of Mine, such as the Indra, although not knowing these divinities to be My forms, I consider his faith as being directed to My bodies or manifestations, and make his faith steadfast, i.e., make it free from obstacles.

Commentary by Sri Sridhara Swami of Rudra Sampradaya:

Amongst those who worship a particular demigod which represents a potency of Lord Krishna then He as paramatma the Supreme Soul within all sentient beings monitoring every thought and action, makes such devotees faith steady and stable. Of others who worship illusory gods, His external potency known as Maya the deluding illusory energy keeps them steadily following the illusion of their erroneous philosophies and speculative theosophies that have no validity not being verified as bonafide in the Vedic scriptures.

Commentary by Sri Madhvacharya of Brahma Sampradaya:

The words yam yam tanum means according to whichever demigod such as Brahma the architect of creation, Indra the celestial chief, or Laxsmi the goddess of wealth. The Narada Purana states: There will be cessation to the votaries of Brahma and others due to their temporary nature; but for the devotees of the Supreme Lord Krishna there is no cessation due to His eternal nature. What is the goal of moksa or liberation from the cycle of birth and death? Where does the atma or soul go after attaining moksa? All these considerations are deliberated upon in the chapters of the Bhagavad- Gita dealing with liberation. Even though the avatars or incarnations of the Supreme Lord are numerous and His expansions are unlimited, moksa is guaranteed and assured to the devotee who devoutly worships any one of them. This has been revealed in the Brahma Vaivartaka Purana.

Commentary by Sri Keshava Kashmiri of Kumara Sampradaya:

If one were to propound that the Supreme Lord is the aggregate of all the demigods and that the demigods are the forms of the Supreme Lord as well. This argument is refuted by Lord Krishna stating yam yam tanum meaning whichever form of demigod or other gods that one craves for some reward seeking to gratify their desires by worshipping or causing others to worship; it is the Supreme Lord only and who keeps the faith of that individual directed towards the very demigod that one contemplates, keeping it firm and steady based upon their latent tendencies from innumerable previous lives. But it should be noted that although Lord Krishna is the Supreme Lord of all, possessing absolute power over everything in existence; He never exerts even the slightest influence over any embodied being to put their faith and devotion in Him.

Commentary by Sri Adi Shankaracharya of Advaita Sampradaya:

7.21 Yam yam, whichever; tanum, form of a deity; yah, any covetous person- among these people with desires; who, being endowed sraddhaya, with faith; and being a bhaktah, devotee; icchati, wants; arcitum, to worship; tam eva, that very; acalam, firm, steady; sraddham, faith; tasya, of his, of that particular covetous person-that very faith with which he desires to worship whatever form of a deity, in which (worship) he was earlier engaged under the impulsion of his own nature-; [Ast. takes the portion ‘svabhavatah yo yam devata-tanum sraddhaya arcitum icchati’ with the next verse.-Tr.] vidadhami, I strengthen.

Commentary by Sri Abhinavagupta of Kaula Tantra Sampradaya:

7.20-23 Kamaih etc. upto man api. On the other hand, those persons, whose minds are conditioned by a variety of their own respective desires for the best and so on (or the desires that may be classified as the best and so on) – they have thier thinking faculty carried away by their desires, and worship a particular deity who possesses nothing but My intermediate body that suits only to those devotees’ desires. Hence, they obtain their desired result from Me alone. But, that result has an end of its own, because it is limited by the mental impressions of their own. Therefore those who perform sacrifice etc., with the aim of becming Indra etc., (or of attaining the houses of Indra etc.) gain their desired fruit accordingly. On the other hand, those whose chief aim is to attain Me, they gain Me alone. But, while the Absolute-being is immanent in all, how is it that the fruit achieved by the worshippers of other deities is limited ? The answer is given as :

Sanskrit Shloka Without Transliteration Marks:

yo yo yam yam tanum bhaktah
sraddhayarcitum icchati
tasya tasyacalam sraddham
tam eva vidadhamy aham

Sanskrit to English Word for Word Meanings:

yaḥ yaḥ — whoever; yām yām — whichever; tanum — form of a demigod; bhaktaḥ — devotee; śraddhayā — with faith; arcitum — to worship; icchati — desires; tasya tasya — to him; acalām — steady; śraddhām — faith; tām — that; eva — surely; vidadhāmi — give; aham — I.