Could you elaborate on the advanced philosophical teachings regarding duality and non-duality found in Chapter 14?

Chapter 14 presents a profound philosophical teaching on oneness, stating that the same essence within one's own body pervades the entire universe. It identifies the intellect that establishes duality, or manifoldness, as pure ignorance that leads to the endless cycle of birth and death. The chapter explains that turning away from this ignorance is the path to attaining oneness. As detailed in Chapter 14, the purification of the mind through a Guru's teachings is essential to realize one's true, non-dual nature. It concludes that everything, from Brahma down to a blade of grass, is ultimately the all-pervading Brahman.