Can you explain the philosophical concepts of oneness (non-duality) and duality as presented in Chapter 14?

Chapter 14 delves into the philosophical concepts of oneness and duality. It teaches that the same divine Essence present in one's own body is the same Essence that pervades the entire universe. True understanding comes from recognizing this oneness in all beings. The chapter explains that holding onto manifoldness, or duality, leads to the cycle of birth and death, and the intellect that establishes this sense of difference is described as 'pure ignorance.' According to the teachings in Chapter 14, the Guru's guidance purifies the mind, allowing one to turn away from ignorance and attain the state of non-duality, where one recognizes that everything, from Brahma to a blade of grass, is pervaded by Brahman.