देहिनोऽस्मिन्यथा देहे कौमारं यौवनं जरा।तथा देहान्तरप्राप्तिर्धीरस्तत्र न मुह्यति॥
dehino ’smin yathā dehe kaumāraṃ yauvanaṃ jarātathā dehāntara-prāptir dhīras tatra na muhyati
Word by word
The verse says
Just as the one who lives in this body passes through childhood, youth and old age, so it passes into another body. The steady person is not shaken by this.
In plain words
This is Krishna's first real argument, and it is cleverer than it looks. He does not begin by asking Arjuna to believe anything new. He points at something Arjuna has already lived through.
You were a child once. That body is gone. Not changed — gone. Almost nothing of it is still here. Then you were young, and that body is going too. You have already survived being replaced, several times over, without once feeling that you ended.
So, Krishna says, you already accept that the body can be swapped out while you carry on. Death is one more swap. He is not asking for a leap of faith. He is asking you to keep counting.
Where you've felt this · in growing older
Find a photograph of yourself at six years old. Not one atom in that picture is still in you. The height is wrong, the voice is wrong, the face is wrong. You would not recognise the child in a crowd. And yet you look at it and say, without hesitating, "that's me." Something has stayed. You have never been able to point at it.
Going deeper
The Sanskrit is doing something precise here. Krishna does not say "you" have a body. He says dehin — the one who dwells in a body, the embodied one. The word already contains the distinction he is arguing for. A dweller is not the house.
The other word to catch is dhīra. It usually gets translated as "wise," but it means steady, firm, unshaken. That is a different quality from cleverness. Krishna is not promising that understanding this will make you smart. He is saying it will make you hard to knock over.
And notice what he does not claim. He does not say grief is foolish, or that you should feel nothing when someone dies. He says the steady person is not muhyati — not bewildered, not thrown into confusion. There is a real difference between sorrow and panic. Arjuna on that chariot floor is not grieving. He has lost his footing entirely. That is the thing Krishna is treating.
This argument is also deliberately modest. It is the first rung of a ladder. Krishna is meeting a man who cannot stand up, and giving him one thought solid enough to hold on to.