Nachiketas, the son of sage Vajasravas, asks Yama to tell him about Agni vidya. Svarga is the place where Yama is not present, so there is no fear in Svarga. The word Svarga here must be interpreted as Sri Vaikuntha, the abode of Lord Vishnu, said Valayapet Ramachariar, in a discourse. Next to death, what human beings fear most is old age. That too is absent in Sri Vaikuntha. Hunger, thirst and sorrow are not present in Sri Vaikuntha. Nachiketas asks Yama to tell him about Agni, which will lead one to Sri Vaikuntha.
The Agni referred to here is Lord Vishnu Himself. Lord Vishnu, because of His leading quality, is Agni. Yama tells Nachiketas that He who is present in all beings is that Agni who leads one to liberation. Yama tells Nachiketas about the Agni present in the sacrificial pit, and also about the size of the pit and the bricks to be used. The bricks spoken of here should not be taken just literally to mean bricks used in construction. There is a symbolic meaning as well, and the reference is to our thoughts. Our thoughts must be of Paramatma.
Nachiketas listens intently to Yama, and the God of Death says the fire in the sacrificial pit will henceforth be known as Nachiketas Agni. He who performs yaga, who gives liberally and who resorts to penance, and who worships Lord Mahavishnu, will not know further births and deaths.
A person who learns through a proper Acharya will be a balanced person, with no strong likes and dislikes. True death is not the departure of life from the body. True death is when we become victims of likes and dislikes. Hating or liking passionately — both lead to unhappiness. This is the death we should fight against, the death caused by our likes and dislikes. He who worships Agni will get rid of this death. Nachiketas receives such instruction and advice from Yama, because of his persistence and commitment to learning from Yama. In the Bhagavad Gita, the Lord gives Arjuna immortal advice, but at the end of it all, He says Arjuna should talk about Krishna’s advice only to those who have the determination to hear the Lord’s words. Arjuna is asked not to talk about it to those who have no desire for such advice.