So Lord Kṛṣṇa, He descends, yadā yadā hi dharmasya glānir bhavati (BG 4.7), just to establish the real purpose of life. When man forgets the real purpose of life, the mission of human form of life, then it is called dharmasya glāniḥ, the disturbance of the occupation of human being. So in that circumstances, out of many, many human being, who awakens, one who awakens the spirit of understanding his position, for him this Bhagavad-gītā is spoken. We are just like swallowed by the tigress of nescience, and Lord, being causelessly merciful upon the living entities, especially for the human being, He spoke Bhagavad-gītā, making His friend Arjuna as the student.
Arjuna was certainly, being an associate of Lord Kṛṣṇa, he was above all ignorance. But still, Arjuna was put into ignorance in the Battlefield of Kurukṣetra just to question about the problems of life to the Supreme Lord, so that the Lord can explain them for the benefit of future generation of human being to chalk out the plan of his life and act in that way so that his life, his mission of human life, can be perfect.
So in this Bhagavad-gītā the subject matter is comprehending five different truths. The first truth is what is God. It is the preliminary study of the science of God. So that science of God is explained here. Next, the constitutional position of the living entities, jīva. Īśvara and jīva. The Lord, the Supreme Lord, He is called īśvara. Īśvara means controller, and jīva, the living entities are... Jīvas, the living entities, they are not īśvara, or the controller. They are controlled. Artificially, if I say that "I am not controlled, I am free," this is not the sign of a sane man. A living being is controlled in every respect. At least, in his conditioned life he is controlled. So in this Bhagavad-gita the subject matter comprehends about the īśvara, the supreme controller, and about the controlled living entities and prakṛti, the nature, the material nature. And next, the time, or duration of existence of the whole universe, or this manifestation of the material nature, and the duration of time, or the eternal time, and karma. Karma means activity. Everything, the whole universe, whole cosmic manifestation is full of different activities. The living beings especially, they are all engaged in different activities. So we have to study from the Bhagavad-gītā, īśvara, what is God, jīva, what are these living entities, and prakṛti, what is this cosmic manifestation, and how it is controlled by time, and what are these activities?
Now out of these five subject matter, in the Bhagavad-gītā it establish that the Supreme Godhead or Kṛṣṇa or Brahman or Paramātmā... You may call whatever you like. But the supreme controller. There is a supreme controller. So the supreme controller is the greatest of all. And the living beings, they are in quality like the supreme controller. Just like the supreme controller, the Lord, He has control over the universal affairs, over the material nature, how the... It will be explained in the later chapters of Bhagavad-gītā that this material nature is not independent. She is acting under the direction of the Supreme Lord. Mayādhyakṣeṇa prakṛtiḥ sūyate sa-carācaram (BG 9.10). "This material nature is working under My direction," mayādhyakṣeṇa, "under My superintendence."