जातस्य हि ध्रुवो मृत्युर्ध्रुवं जन्म मृतस्य च।तस्मादपरिहार्येऽर्थे न त्वं शोचितुमर्हसि॥
jātasya hi dhruvo mṛtyur dhruvaṃ janma mṛtasya catasmād aparihārye ’rthe na tvaṃ śocitum arhasi
Word by word
The verse says
Whatever is born will certainly die, and whatever dies will certainly be born. There is no way around this, so you have no reason to mourn.
In plain words
The second argument, and it needs no belief at all.
Things that are born die. That is not a doctrine; it is a description. Krishna adds the return half — what dies is born again — but even without it the first half stands on its own.
The key word is aparihārya — unavoidable. Not acceptable. Not good. Unavoidable.
Where you've felt this · in growing older
The diagnosis is not going to change. Every arrangement you can make is on this side of it. At some point the energy going into wishing otherwise has to be let go, not because you have made peace with it, but because it was never doing anything.
Going deeper
This is the Gita at its most unadorned, and the argument is available to anyone.
It makes no claim about souls or rebirth that you have to accept to feel its weight. The first half is simply true: everything born ends. Grief over that specific fact is grief over the terms of existence.
The Gita is not saying do not feel it. Krishna never says that anywhere. What he says is na tvaṃ śocitum arhasi — you have no warrant for grieving, no ground to stand on. It is closer to this is not the injustice you are treating it as than to stop feeling.
What this does for Arjuna specifically is dismantle a hidden assumption in his Chapter 1 speech. He has been talking as though the deaths of Bhishma and Drona are something he will introduce into the world. They are not. They were already coming.
The war changes when and how. It does not change whether. That is a much smaller kind of authorship than the one crushing him.