Can you explain the philosophical distinction between oneness and duality as presented in Chapter 14?

Chapter 14 of the Sai Satcharitra delves into the philosophical concepts of oneness and duality. It teaches that the intellect establishing duality, or seeing separation between things, is a form of "pure ignorance" that leads to the endless cycle of birth and death. Conversely, turning away from this ignorance leads to the attainment of oneness. The chapter states that the same divine Essence that is in one's own body is present in the entire universe. As the text explains, everything from Brahma down to a blade of grass is pervaded by Brahman, the Supreme Reality, and recognizing this non-duality is the path to realizing one's true nature through the purification of the mind.