How does Chapter 14 explain the concepts of duality and non-duality, and what is the role of the Guru in achieving the state of oneness?

Chapter 14 provides deep philosophical teachings on duality and non-duality. It states that the intellect establishing duality is pure ignorance, and holding onto this manifoldness leads to a cycle of birth and death. The path to liberation is through attaining oneness, which is turning away from ignorance. The Guru's teachings are crucial in this process, as they bring about the purification of the mind. Through this purification, one realizes their true nature and understands that the same Essence in one's body is present in the entire universe, with Brahman pervading everything from Brahma to a blade of grass.