The fifth mantra takes up this question, it says that actually prana, which are the life forces, even they are not really responsible for life. No mortal lives by prana or apana but all live by something else due to which these two find asylum. Why dragon, atman, Brahman consciousness isn't enough to explain life? You have a mind-body system and that's it. That's the fifth mantra - we'll read that now.
Swami Sarvapriyananda teaches the Katha Upanishad, one of India's most revered texts which is also a part of the Vedas. It is a collection of philosophical poems representing a conversation between the sage Naciketas and Yama (god of death). They discuss the nature of Atman, Brahman and Moksha(liberation).