A sage named Vājaśravasa, preparing to perform the viśvajit sacrifice, begins giving away his cattle. His son Nachiketa, a boy, watches. The cattle his father is donating are old, barren, blind — they have given up their milk and cannot calve. The son understands that this is not generosity. It is disposal.
The boy asks, Father — and to whom will you give me? Vājaśravasa ignores him. The boy asks again. And again. Finally the father, impatient, says — I will give you to Yama. The god of death.
The boy takes it seriously. He walks to Yama's house. He finds it empty — Yama is out. So he waits. Three days. No food, no water, nothing.
When Yama returns, he is ashamed. A guest, a brāhmaṇa's son, has been neglected at his threshold for three days. To atone, he offers the boy three boons.
The first boon is small. Nachiketa asks that his father, when he returns home, should not be angry with him, and should recognise him as his own son. Yama grants it.
The second boon is measured. Nachiketa asks for the fire-ritual that leads to the heaven where there is no hunger, no thirst, no grief. Yama teaches him the ritual in detail. The fire is named after him — the Nāciketa fire.
The third boon is the one the text has been waiting for. Nachiketa says — when a man dies, there is a doubt. Some say he exists after. Some say he does not. Teach me the truth of this.
Yama recoils. This is too deep, he says. The gods themselves have doubted it. Ask something else. Ask for long life. Ask for wealth. Ask for sons and grandsons and elephants and gold. Ask for empires. I will give you anything but this.
The boy does not move. He says — these things you offer are temporary. They end in you. What I asked for is what you cannot give and cannot refuse. Teach me. I will not take anything else.
Yama recognises the student. And he teaches. The ātman is not born. It does not die. It was not produced from anyone, and no one was produced from it. Unborn, eternal, ancient, it is not slain when the body is slain. Smaller than the small, greater than the great, it sits in the heart of every creature.
The Kaṭha Upaniṣad, which follows, is this teaching in detail. Its power is not in the teaching alone — the teaching has been spoken elsewhere. Its power is that we have watched the boy ask. We have seen him refuse the wealth. We have seen him be brave enough to stand at death's door and not take anything less than the answer.
A teaching, the Upaniṣads know, only lands when the asker has earned it. Nachiketa earned it by being willing to wait three days in front of the house of death, and then refusing to be diverted.