Till 19th sloka, Sri Krishna described the greatness of His devotees. Devotee, who considers Sri Vasudeva, as everything -vasudevamidhisarvam. But such a devotee is very hard to find. Such a devotee was Prahalada and we have come to this Kshetram to see Prahalada's favourite Sri Narasimha. From 20th sloka, in eight slokas, the Lord regrets that while He was there to grant anything, people swarm around other gods to seek favour. Though Sri Krishna could grant anything, He does not grant the cheap desires that easily nor quickly. But many people want such transient and temporary needs and so they seek other gods, who readily grant them. But, this power to grant such needs has been delegated by the Lord to these gods. The Lord resides in every god , and as the controller and commander inside, He makes them to satisfy the needs of people. Now the sloka 21:
yo yo yam yam tanum bhaktah
tasya tasyacalam shraddham
tam eva vidadhamy aham
"I am in every demigod’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."
yo yo bhakta = such devotees , yam yam tanum = [approaching] such [gods who are the Lord's] body [or who are controlled by the Lord]. Shraddhaya =with dedication, arcitum = to do pooja, icchati = desires. Devotees approach the many gods , who are all the body of the Lord [just like soul is the master of the body] and desire to perform poojas to them to get their desires full filled. Tasya tasya = such devotees, acalam = unshakable, shraddhaam = faith in those gods, aham = I [ Sri Kishna], vidadhami = establish [ in them]. The Lord says that He ensures that these people have unfaltering faith in those gods. Arjuna got a doubt here. The Lord earlier told that all should worship the Lord as He alone is capable of granting anything and everything, then why should He encourage these people to go to these gods who can never grant the highest reward of Moksham? Sri Krishna is going to clear this doubt in this and the next sloka. Here we have to understand that all gods are body of the Lord. We can worship anyone, but none of them are independent. Inside them the Lord resides and controls and commands them. He delegates certain power to each of them, which they could grant to people approachng them. A servant serves the King. He is not intelligent enough to know that atman of the King is pleased by his services. He only knows that by serving, the King is pleased and he grants some money for his living. Actually, atman of the king is pleased and that atman directs the body to take out money and grant to the servant. Similarly, these gods are mere bodies of the Lord and He commands them to grant certain needs to those who sseek those gods. These people are expected to be loyal to those gods. These gods also do not have total knowledge that the Lord is in them and that they have drawn their powers only from Him. Here this hill, where the Lord Sri Jwala Narasimha is , is called Achala Meru chaya parvatam - shadow of the great Meru mountain. Nammalwar says that in infinite births we have been going after various gods for various needs. They grant only temporary satisfaction.