The Preface mentions that the principle of needing a Sadguru is ancient and supported by Vedic scriptures. Can you provide the specific Vedic scriptures it references?

While the Preface by Balkrishna Vishwanath Dev does state that the principle of needing a Sadguru for salvation has existed since Vedic times and is supported by Vedic scriptures, it does not actually name or quote any specific Vedic texts to support this claim. Chapter 0 makes this assertion to establish the ancient origins of the Guru-disciple tradition. The text then moves on to quote extensively from a later work, Shri Dnyaneshwari by Dnyaneshwar Maharaj, to elaborate on the nature of serving a Guru. Therefore, the specific Vedic references you're asking about are mentioned as a category but not detailed in this section of the book.