But Nachiketa replied that material things will last only ephemerally and would not confer immortality. So, no other boon would do. Yama was secretly pleased with this disciple and elaborated on the nature of the true Self, which persists beyond the death of the body. The key of the realization is that this Self is inseparable from Brahman, the supreme spirit, the vital force in the universe. Yama's explanation is a succinct explication of Hindu metaphysics, and focuses on the following points: