What fundamental principle about salvation is presented in the preface, and what are its historical roots?

The preface, or Prastavana, of the Shri Sai Satcharita opens by stating a foundational belief in the land of Aryavarta. As explained in Chapter 0, this is the firm principle that there can be no salvation without the grace of a Sadguru. The text emphasizes that this is not a modern idea but a very ancient one. Its origins are traced back to the Vedic times, and the principle is said to be supported by the Vedic scriptures, highlighting its deep-seated importance in the spiritual tradition.