Baba uses an analogy about a gem and a stone being polished. What was he trying to explain with this comparison?

In Chapter 19, Sai Baba uses the analogy of a gem and a stone to explain the importance of a disciple's inherent qualities, specifically faith and patience. He points out that both a stone and a gem may be subjected to the same polishing process on a whetstone. However, their final states are vastly different: "the stone remains a stone, but the gem becomes a brilliant jewel." Baba uses this to illustrate that while a Guru's guidance (the polishing) is applied equally, the outcome depends on the disciple's readiness and inner nature. A disciple with strong faith and patience, like the gem, can be transformed into something brilliant. In contrast, a person without these qualities, like the stone, may be smoothed but cannot gain the same spiritual luster. It highlights that a Guru expects "strong faith at the Guru’s feet and the strength of courage which is patience" for his teachings to be truly effective.