Can you explain the analogy of the stone and the gem from Chapter 19 and what it teaches about the disciple's journey?

The analogy of the stone and the gem, found in Chapter 19, serves as a powerful metaphor for the outcomes of spiritual practice under a Guru. It explains that while the Guru's guidance, like a whetstone, is applied equally to all disciples, the results vary based on the disciple's inherent nature. As the text describes, when both a stone and a gem are rubbed on the whetstone, "the stone remains a stone, but the gem becomes a brilliant jewel." This illustrates that a disciple with the inherent quality of a 'gem'—possessing receptivity, virtue, and potential—will be polished into a sparkling diamond by the Guru's teachings. Another individual, the 'stone,' may become smoother but cannot attain the same luster, suggesting that the disciple's own inner readiness and quality are crucial for transformation.