Bhagavad Gita Chapter 2 Verses 13
dehino ’smin yathā dehe kaumāraṁ yauvanaṁ jarā
tathā dehāntara-prāptir dhīras tatra na muhyati
Word to word meaning
dehinaḥ—of the embodied;
dehe—in the body;
na muhyati—are not deluded
Just as the embodied soul continuously passes from childhood to youth to old age, similarly, at the time of death, the soul passes into another body. The wise are not deluded by this.
Lord Krishna explains to Arjuna that the soul is not perishable and it is the body that is perishable. The soul just departs from the destroyed body to another new body. So here the soul is getting something new and it’s a pint to rejoice and not to cry and depending upon the good deeds that we have done we are bound to get a better body. So great and just people like the great Bhishma and Acharya Drona will definitely get a good body or even a heavenly body so that they can always remain close to the supreme Lord
He also explains that even when the soul is in the same body the soul does not undergo any transformation but the body undergoes changes every minute and every second. When we breathe each cell gives out carbon dioxide and takes in oxygen and all the internal structures undergo transformation. Every day old cells are discarded and a new cell is replaced. In a period of seven years, about 98% of our cells get replaced. Still, the soul is the same. So for the soul when it is residing in the same body itself for it’s like residing in a new body every second but it never changes. Finally when the body goes to a state where the soul can’t stay it changes its body.
Our body undergoes many transformations from infant to childhood then youth and finally old age but the soul does not change
The soul is the body dweller and it dwells in a body. If it finds it’s old body not worth living it changes its body. It’s just like a person living in a house. The person living in that house will be the same but the house undergoes transformations. For minor changes, you repair your home by yearly painting and maintenance. As days go by the structure of the building itself becomes weak and at a point, it is not worth for dwelling so you shift to a new home. The new home you get depends on the good deeds that you have performed in your old home. If you had been active and had earned a lot of money in the legal way you will permanently get a good and big home. If not you will have to settle in a small home depending on what you earned in your old home
Likewise, it’s the karma that gives you a good body. If you had done good deeds in your old body you will get a good life in your new body. This explains why some of them are born rich while others are born poor. It’s their previous births karma that makes God decide which body you have to be in. Your good deeds or karma is put in god’s bank and when your body is damaged he checks your account in his bank and based on what karma you have deposited you will get a good birth or bad
So Lord Krishna says don’t cry Arjuna for Grandsire Bhishma and Acharya Drona are bound to get a good life after this birth for the good karma they had deposited in God’s bank.