Arjuna says:
My Supreme Lord, what is that Brahman? What is the adhyātma? What is meant by karma? What is the adhibhūta? And who is said to be the adhidaiva?

Who is the adhiyajña and how does He exist in this body, O Kṛṣṇa? And how are You to be known at the time of death by the self-controlled?

Lord Kṛṣṇa says:
Brahman is the Supreme that does not change or decay. One’s own inherent nature is said to be the adhyātma, and the creative force which gives rise to material beings is known as karma.

The adhibhūta is the material world which perishes, the adhidaivata is the cosmic governing deity, and it is I Myself who is the adhiyajña present in the body.

And the one who leaves his body at the time of death and contemplates upon Me alone, without doubt reaches Me.

Arjuna, whatever state one remembers when leaving the body, that state one will certainly attain after death. For a person’s condition is the inevitable result of what has been dwelt upon throughout one’s life.

Therefore, ever mindful of Me at all times, fight. With your mind and intellect dedicated to Me, you will be free of doubt and shall surely come to Me.

O Arjuna! With the mind absorbed and constantly engaged in yoga, without thinking of anything else, one reaches the Divine Supreme Being.

One should meditate on the all-knowing Supreme Person. The one who is the oldest and supreme Controller of all. His form is inconceivable, more subtle than an atom, and the maintainer of everything. He is brilliant like the Sun and beyond all darkness.

At the time of death one should dwell in a state of devotion and with the strength of yoga, one should maintain an unwavering mind. Keeping the life force between the eyebrows in the proper way, one reaches that Divine Supreme Being.

I shall now explain that goal, which the knowers of the Vedas call the Imperishable. Those ascetics who are free from desire enter into it, and due to their aspiration for perfection they take vows of celibacy.

Having closed all the entrances of the body, focusing the mind within the heart, fixing the life force within the head, one should be engaged in yoga practise with steady concentration.

Chanting the sacred syllable oṁ which embodies the Absolute, thinking of Me constantly one abandons the body and leaves the world, thereby reaching the supreme goal.

O Arjuna, I am easily attainable by that steadfast practicing yogī who is constantly mindful of Me, not thinking of anything else.

Having reached the highest perfection and attaining Me, the great ones never again take rebirth in this world which is transient and full of misery.

Rebirth is inevitable right up to the world of Brahmā. But after attaining Me, Arjuna, there is no rebirth.

Those who know the duration of a cosmic Day and Night understand a Day of Brahmā lasts for a thousand Mahā-yugas and a Night of Brahmā lasts for another thousand Mahā-yugas.

At the beginning of a Day of Brahmā all beings come forth from the unmanifest, and when the Night comes, they are dissolved back into the unmanifested state.

These same beings come forth again and again, and helplessly they are withdrawn at the coming of the Night. When the next Day begins, yet again they manifest.

There is, however, another unmanifested realm which is superior to this unmanifest place of the material world; it is eternal and does not get destroyed when all other living beings pass away.

This unmanifest realm is also called ‘The Imperishable Realm’. It is the highest goal from which one does not return; it is My Supreme Abode.

The Supreme Being is attained by unswerving devotion, Arjuna. He is the One in which all beings exist and by whom this whole universe is pervaded.

Arjuna, now I will describe to you the different times of leaving this world. One in which the yogī does not return and the other in which they do.

The knowers of Brahman attain that Supreme and leave during the influence of the fire deity (Agni), the day, the bright fortnight, or during the six months of the northern course of the Sun.

But the yogī who leaves during the smoke (absence of the fire deity), the night, the dark fortnight, or the six months of the southern course of the Sun, reaches the light of the Moon and then returns.

Therefore, understand there exist two eternal paths of departure, the light and the dark. By following the path of the light one does not come back, but by following the dark, one returns.

But Arjuna, the true yogī who knows these two paths is never bewildered. Therefore, O Arjuna, at all times engage yourself in yoga.

Whatever merits are gathered from the study of the Vedas, from the performance of sacrifices, or from the practise of austerities and charity, all of it is transcended by the yogī who knows this teaching of Mine; he reaches the Original, Supreme Abode.