How does the relationship between a gem and a stone illustrate the importance of a disciple's inherent qualities?

Chapter 19 uses the analogy of a gem and a stone on a whetstone to illustrate a Guru's expectations. While the same process of polishing is applied to both, 'a stone remains a stone, but the gem becomes a brilliant jewel.' This metaphor suggests that while a Guru provides guidance and 'polishes' all disciples, the outcome depends on the disciple's own nature and effort. A Guru expects the disciple to possess the inherent qualities of a 'gem,' which are 'strong faith at the Guru’s feet and the strength of courage which is patience.' Without these fundamental virtues, even the best guidance cannot transform a 'stone' into a 'sparkling diamond.'