There's an analogy about a stone and a gem both being polished. What is this trying to teach us about a Guru's role and a disciple's potential?

This analogy, found in Chapter 19, explains the dynamic between a Guru's efforts and a disciple's inherent nature. Both a stone and a gem can be subjected to the same polishing process on a whetstone. However, the gem becomes a brilliant, sparkling diamond, while the stone merely becomes smooth. A stone cannot gain the luster of a gem. This illustrates that while a Guru provides guidance and 'polishing' for all, the disciple's transformation depends on their own innate quality. The text states that a Guru expects the disciple's wisdom, strong faith, and the courage of patience. Without these gem-like qualities, the Guru's teachings cannot produce the same brilliant result.