Krishna speaks of reincarnation

The Two Paths
When Arjuna appeals for help, he is not asking for a knowledge of the Universal Self, nor for freedom from the limitations of the world. He wants to know what to do: he is caught in a dilemma, each branch of which is disaster and misery for him and for his world.

In most of the Upaniṣads, on the other hand, the inquirer is one who seeks to know the truth about the universe, or the truth about himself.

The wife Maitreyi who liked to talk about Brahman (no prejudice against women in the Upaniṣadic tradition) rejects offers of property and says: ‘What should I do with that which will not make me immortal? Tell me that which you know, which gives immortality’. (Bṛhadāraṇyaka Upaniṣad)

Nachiketas refuses similar offers of distraction: ‘These things last but till tomorrow. Tell me the secret of death – this is the only boon Nachiketas asks’ (Kaṭha Upaniṣad)

These are calm, determined people, who have turned their back on very favourable opportunities, and are bent on knowing the answer to the riddle of the universe and themselves. Some of them have given long service to the teacher, or have proved the strength of their desire to know by terrifying austerities, such as confronting death face to face.

Arjuna’s situation is quite different. He is in an emotional crisis, and can see no possible outcome where he could be happy. He is not detached from the world, only crushed by this bit of it. He has not done service to the teacher, only appealed to him impulsively. But there is one point of resemblance: he is desperate. He is willing to do anything, as they are willing to do anything. For this reason the first chapter of the Gītā is called the Yoga of Despair. It differs from mere despair, which is paralysing, because Arjuna appeals to Kṛṣṇa for help. Hope has not been entirely lost. Despair can be turned into a yoga or means when it becomes desperation. As such, the teacher Kṛṣṇa takes advantage of it.

As has been said, he first reminds Arjuna of worldly considerations like his honour as a warrior: this has no effect now. Arjuna has been quoting the words of sages who speak of the disastrous effects of fighting, and the greatness of absolute pacifism.

Kṛṣṇa then speaks of reincarnation.

II.12 Never did I not exist,
Nor you, nor these great ones,
Nor shall we ever cease to be.
Any of us, in the future.
13 As in this life, all beings
Pass through childhood, youth, and age;
In the same way, they pass to another body.
The wise are not confused by such changes.

And again:

II.22 As the wearer casts off worn-out clothes
And puts on himself others which are new,
Even so casting off worn-out bodies,
The body-wearer passes on to new ones.

But Arjuna’s distress is too pressing for distant perspectives to relieve it. Kṛṣṇa advises him that his path should be one of action rather than renunciation