The Lord of Death told the boy to ask for a different boon ‘because the Atman-philosophy is something which can confuse even the divines’. But the boy was smart enough for that.
He says: “By the very fact you are categorising it like this, it must be great. So nothing else would be equivalent to that boon which I am seeking. Please give it to me. There is nobody else who can equal you in teaching this to me.”
Yama tries different artifices to convince the boy. “I will grant you lots and lots of elephants, horses, treasures, land, kingship, sons and grandsons, life as long as you wish.
Whatever you desire I will grant it. I will send my own men to run your chariot and to play music for you. Please don’t press for your boon. Ask anything else” says Lord Yama.
All this is a test. He forces a golden necklace on the boy. Nothing tempted the boy Naciketas.
“What all you are giving will one day return to you. I want only that which will be permanent, ever. I want only that. This Naciketas will not take anything else!”—says the boy most emphatically.
The golden necklace is not even touched by him.