How does Chapter 18 describe the fundamental nature of the Sadguru and the effect of receiving His grace?

Chapter 18 extols the Sadguru as the supreme, eternal, and beginningless one, who is beyond duality and imperfection. It poetically describes a devotee approaching the Guru as being like a salt doll entering the ocean—it merges completely and cannot return. The text emphasizes that when a person is fortunate enough to receive the Guru's grace, the false distinctions of 'mine' and 'thine' disappear. The Guru is presented as the manifest form of God, encompassing Brahma, Vishnu, and Maheshwara, and the sole teacher of Self-knowledge.