Early hindus were nomadic. Fire was central in their life. Fire was worshiped and was offered sacrifices into it. This led to rituals and mantras. Later rituals and mantras became central. This trend was doubted by a young boy nasikedhas. He asks questions.
Vajravasis was a rich man he was involved in fire rituals
His son was nasikedhas. He develops doubts about father's rituals
He asks his father about the futility of the sacrifices, and gets improper reply.
He decided to ask lord yama about it.
He asked yama about the ritual that takes him to heaven
Yama replied that the fire that is needed for the homa is in the cave of mind.It has to be done thrice, with the help of three people, father,mother and teacher.with three steps, discipline,thinking and prayer
nasikedhas asks yama about the ways to win over death
yama tests nasikedhas's intentions
nasikedhas demonstrate his absolute lack of desire for worldly pleasures
yama is satisfied and grants him the way to win over the death.
while giving away gifts as part of the rituals, he gives useless cows which do not give milk anymore. Nachiketas does not doubt his fathers rituals...he feels bad that the rituals will not bear fruit,because his father is giving old and worn out cows to people which is sin. So to protect his father from this sin, he wants to offer himself as gift and hence asks his father, whom he is going to be given to. For which his father replis in anger (since he was busy with the ritual and did not have time to reply to his young sons silly questions) 'to yama'.
Thus Nachiketas goes to yama to fulfil his fathers words and gets enlightened.
Kathopanishad does not talk or question about rituals. Its only questoins about life after death and the 'atman'.
1. The ritual parts of Vedas - Brahmans 2. The upanishad parts.
Brahmanas insist on the ritual parts for day to day necessaity as it is an excahnge process between the Devas and Humans.ButBrahmanas themselves say us to cross that part and go to Veda anta ie upanishads.
Lord Krishna himself in Geeta scolds people who only do rituals as " Veda Vada radha" ( useless people highlighting the benefit of rituals and not crossing that stage)
The Meemamsa and Karma Margis who propoagated the ritual part were severely condemned by Adisankara himself.
This dosenot mean that rituals to be condemned. They are part of vedas. But doing only rituals and not progressing to the next stage is condemned.
rituals are basics. We teach our child 2+ 3 is 5 as take 2 in left hand, three in right hand and count. If the child continues it even at 10th std and tell that it is how i was taught, That is stupidity.
Rituals are preparatory and benefits the Devas. One has to cross that stage to realise the Atman and Brahman.
Upansihads are the finals and they condemn doing only rituals without realising the supreme.
Siddars say the same " natta kallum pesumo, Nadan ul irukkayil" But one need to worship that kal initially and progress to the next stage that the nadhan is in ul.
actually upanishads are part of the vedas themselves.
We lost many parts ( shakas) of vedas but few upanishads of that part have survived. The Upanishads are as old as vedas themselves.
Nasiketas questions his father as he was giving useless cows as offerrings. He questions his father for his disbelief in rituals. He asks him - now you have given all the old cows to Brahmins and whom you will offer me. The Father angrily replies that i have offered you to Yama. Nasiketas starts to meet Yama as an offerring. ( Not as soul which is dead) and waits for 3 days without food as yama was away.
Since a guest was without food for 3 days, yama offers him 3 boons. Nasiketas uses the 3rd boon as a question - from where Yama explains. It is yama who explains the upanishad part.
Naskiteas wanted that boon - a question on after life-even when yama offered him so many things but nasiketas insisted on that. The futality of focusing only on rituals is explained by Lord Yama.
Upanishads have opened up the various schools - Advaita, saiva siddanta etc