Text 61 

ishvarah sarva-bhutanam
hrd-dese ’rjuna tishthati
bhramayan sarva-bhutani
yantrarudhani mayaya

Translation

The Supreme Lord is situated in everyone’s heart, O Arjuna, and is directing the wanderings of all living entities, who are seated as on a machine, made of the material energy.

Commentary by Srila Prabhupada 

Arjuna was not the supreme knower, and his decision to fight or not to fight was confined to his limited discretion. Lord Krishna instructed that the individual is not all in all. The Supreme Personality of Godhead, or He Himself, Krishna, as the localized Supersoul, sits in the heart directing the living being. After changing bodies, the living entity forgets his past deeds, but the Supersoul, as the knower of the past, present and future, remains the witness of all his activities. Therefore all the activities of living entities are directed by this Supersoul. The living entity gets what he deserves and is carried by the material body, which is created in the material energy under the direction of the Supersoul. As soon as a living entity is placed in a particular type of body, he has to work under the spell of that bodily situation. A person seated in a high-speed motorcar goes faster than one seated in a slower car, though the living entities, the drivers, may be the same. Similarly, by the order of the Supreme Soul, material nature fashions a particular type of body to a particular type of living entity so that he may work according to his past desires. The living entity is not independent. One should not think himself independent of the Supreme Personality of Godhead. The individual is always under the Lord’s control. Therefore one’s duty is to surrender, and that is the injunction of the next verse.

Commentary by Sri Visvanatha Cakravarti Thakur

Having stated the views of the propounders of innate nature (svabhava) in two verses, the Lord now states his own view. The Lord, Narayana, is the antaryami.

yah prthivyam tisthan prthivya antaro, yam prthivi na veda, yasya prthivi sariram, yah prthivim antaro yamayati

He is situated within the earth. The earth does not know him. The earth is his body. He controls the earth from within. Brhad Aranyaka Upanisad 3.6.3

yac ca kincij jagaty asmin drsyate sruyate 'pi va antar-bahis ca tat sarvam vyapya narayanah sthitah

Narayana is spread everywhere inside and outside of everything seen or heard of in the universe. Mahanarayana Upanisad 13.5

As is stated in these srutis, the Lord is situated in the heart. What does he do? By his own sakti (mayaya) he makes all living entities engage in their respective actions (bhramayan). The living entities, like artificial dolls attached to a device with strings, are made to move by maya. Or another meaning is: all living entities mounted in their bodies are made to move by maya.