How does the analogy of the stone and the gem illustrate the role of a disciple's inner qualities?

The analogy of the stone and the gem, found in Chapter 19, is a profound metaphor for spiritual development. Both a stone and a gem can be rubbed on a whetstone, representing the Guru's guidance. However, only the gem becomes a brilliant jewel, while the stone merely becomes smooth. This illustrates that the Guru's teachings are available to all, but the outcome depends on the disciple's inherent nature. A disciple with the innate qualities of strong faith and patience—the 'gem'—can be polished to brilliance, whereas a disciple lacking these virtues—the 'stone'—cannot attain the same spiritual luster, despite receiving the same guidance.