Fire is regarded as "the foundation of all the worlds," because it is the revealer of creation. If there were no fire or light, no manifested form would be visible. We read in the Semitic Scriptures, "In the beginning the Lord said, 'Let there be light."' Therefore, that which stands in the external universe as one of the purest symbols of the Divine, also dwells in subtle form in the heart of every living being as the vital energy, the life-force or cause of existence. Yama now tells Nachiketas how, by performing sacrifice with the three-fold knowledge, he may transcend grief and death and reach heaven. The three-fold knowledge referred to is regarding the preparation of the altar and fire. Nachiketas being eager to learn, listened with wholehearted attention and was able to repeat all that was told him. This so pleased Yama that he granted him the extra boon of naming the fire-sacrifice after him and gave him a garland set with precious stones. Verses XVI-XVIII are regarded by many as an interpolation, which would account for certain obscurities and repetitions in them. XX Nachiketas said: There is this doubt regarding what becomes of a man after death. Some say he exists, others that he does not exist. This knowledge I desire, being instructed by thee. Of the boons this is the third boon. XXI Yama replied: Even the Devas (Bright Ones) of old doubted regarding this. It is not easy to know; subtle indeed is this subject. O Nachiketas, choose another boon. Do not press me. Ask not this boon of me. XXII Nachiketas said: O Death, thou sayest that even the Devas had doubts about this, and that it is not easy to know. Another teacher like unto thee is not to be found. Therefore no other boon can be equal to this one. XXIII Yama said: Ask for sons and grandsons who shall live a hundred years, many cattle, elephants, gold and horses. Ask for lands of vast extent and live thyself as many autumns as thou desirest. XXIV If thou thinkest of any other boon equal to this, ask for wealth and long life; be ruler over the wide earth. O Nachiketas, I shall make thee enjoyer of all desires. XXV Whatsoever objects of desire are difficult to obtain in the realm of mortals, ask them all as thou desirest; these lovely maidens with their chariots and musical instruments, such as are not obtainable by mortals--be served by these whom I give to thee. O Nachiketas, do not ask regarding death.