KATHOPNISHADA CHAPTER 1 SHLOKA 13

                     

                                               स त्वमग्निँ स्वर्ग्यमध्येषि मृत्यो

                                                प्रब्रूहि त्वँश्रद्दधानाय मह्यम् ।
                               
                                                 स्वर्गलोका अमृतत्वं भजन्ते
                           
                                                एतद् द्वितीयेन वृणेवरेण ॥ १३

                       SA TWAM AGNIM SWARGAM - ADHYESHI MRUTYO

                         PRABRUHI TWAM SHRADHADHANAY MAHTAM |

                             SWARGALOKA AMRUTATWAM BHAJANTE

                                   ETAD DWITIYEN VRUNE VAREN || 13

    OH DEATH ,YOU KNOW THE FIRE WORSHIP - YADNYA THAY LEADS TO HEAVEN

   EXPLAIN TO ME THAT BY WHICH THOSE ATTAINS IMMORTALITY -I PRAY TO YOU

                                                THAT AS MY SECOND BOON -13

      In this Shloka Nachiket is asking for second boon . He did ask for a boon that was personal and helped his father  and the family . Now he is asking for the second boon . This may be little confusing as in this one he is asking for immortality in Heaven. He is asking for the knowledge to get to Heaven . Many of us do the spiritual exercises  and also do the rituals like the Yadnya  and also try to donate money and do good acts . All of them are considered as sacrifices, though they are not in true sense FIRE worship or the so called Yadnya. But they are all done with Desire to be in Heaven for ever or achieve the mortality .
    So this question is to help people understand what they can do to get to the higher level though not the highest level . One of the concept of heaven is that there is no sorrow  and there is immortality. I am not sure if theses are correct . but if one looks  any ABRAHAMIC RELIGIONS they all have similar concept. You do this  and You will be in heaven. You do that and you will be in hell. In Hindu concepts for many it is similar. and one does this  and that and you will have great life after this mortal life  and if you don't do it you will have bad afterlife . I am not sure if that is correct , but at least here Nachiket is asking a question as to what one should do to have great after life in Heaven  and achieve immortality .
   (My concept of heaven is that of ASTRAL WORLD is that one has both Causal body and astral bodies  and also mind , intellect, Chitta  and ego. Depending upon the desires  and karma , this place is good or bad or worse . But it is a stop over, just like at airport, if you have First class ticket or you are member of smoke club , you get to get in a special room and have food  and may be drink . So if one has done good deeds he will have good after life  and he will understand the mistakes that he has done  and then when he runs out of 'Chips' ' like in casino , he will have to leave the Astral world  and come to mortal world.Again the desires  and debt  etc will also decide the life  and the duration of the stsy in so called Heaven . )

KATHOPNISHAD CHAPTER 1 SHLOKA 12

                                           
                                              स्वर्गे लोके न भयं किंचनास्ति
     
                                                न तत्र त्वं न जरया बिभेति ।

                                               उभेतीर्त्वाऽशनायापिपासे

                                               शोकातिगोमोदतेस्वर्गलोके ॥ १2
                            SWARG LOKE NA BHAYAM KINCHANASTI

                              NA TATRA TWAM NA JARAYA BIBHETI

                                  UBHE TITVAR ASHANAYA PIPASE

                           SHOKATAGAH  MODATE SWARG LOKE || 12

IN HEAVEN THERE IS ANY FEAR.NOR ANY OLD AGE THAT ONE FEARS YOU ARE NOT

                         THERE . HAVING CROSSED THE THIRST AND HUNGER

                                 ,ONE REJOICES ABOVE GRIEF - SORROW||12
         In this Shloka , Nachiketa is describing the usual concept of the heaven . This is not limited to Vedic Religion, but also to many other . One or different way the Christianity and Muslim  religion describe same type of conditions in heavens. In heaven there is no hunger, thirst, or aging process etc . Again one has to realize that  when one dies on earth, there is no physical body and so there is no physical body associated qualities . The the aging  occurs to physical body, the hunger is part of physical body and same is true for thirst. Without the physical body these things can not exist.He also tells the YAMA or the God of Death that YOU ARE NOT THERE - which means Death is not there in heaven . This is a concept in some religions  and not 100 % accurate in Vedic religion.
      In Vedic concept of the heaven , there are levels of ASTRAL WORLD. In the lower levels there is sorrow  and some suffering . But again there is no physical body. So the suffering must be that of mind . But in higher levels there is better situation . Only in higher levels - 6th and 7th level , one is not going to be reborn and they are as close to eternity as possible without being one with HIM. One can compare this to like going in to casino , We go there with money -chips  and when we run out of money or chips , we have to leave  and live our usual life. So one goes to Astral world till his CHIPS of Punya are exhausted and also his desires  and attachments and lust will send him back to the world of physical body .