What is the traditional Indian belief about achieving salvation, as mentioned in the preface of the Satcharita?

According to the preface in Chapter 0, there is a foundational and ancient belief in the land of Aryavarta, existing since Vedic times, that there can be no salvation without the grace of a Sadguru. This principle is not new but is deeply rooted in the culture and supported by scriptures. The text emphasizes that the path to this grace is through service, as exemplified by the teachings of Lord Samarth Sadguru Dnyaneshwar Maharaj, who described how serving the saints with one's entire being is the key to attaining knowledge and, ultimately, salvation.