What are the philosophical teachings on duality and non-duality presented in Chapter 14?

Chapter 14 delves into the philosophical concepts of oneness and duality. It teaches that the Essence within one's own body is the same as the Essence in the entire universe. He who surrenders to this Essence understands oneness, whereas clinging to 'manifoldness (duality)' leads to the cycle of birth and death. The chapter defines an intellect that establishes duality as 'pure ignorance.' The path to purification and realizing one's true nature is through the Guru's teachings. As explained in Chapter 14, turning away from ignorance is how one attains oneness, as even a 'trace of difference in the mind' prevents the state of non-duality. It concludes that everything, from Brahma to a blade of grass, is pervaded by Brahman.