What is the meaning behind Sai Baba's analogy of the gem and the stone being polished on a whetstone?

Sai Baba uses the analogy of a gem and a stone to illustrate the importance of a disciple's inherent qualities and readiness. As explained in Chapter 19, both a stone and a gem undergo the same polishing process on a whetstone. However, while the stone merely becomes smooth, the gem transforms into a brilliant jewel. This comparison highlights that even with a powerful Guru providing guidance (the polishing), the disciple's inner potential and qualities, specifically strong faith and patience, determine the outcome. A disciple without these virtues is like the stone, unable to gain the luster of a gem despite the Guru's efforts.