Explain the analogy of the stone and the gem used in Chapter 19 in the context of a Guru's teachings.

Chapter 19 uses the analogy of a stone and a gem to illustrate the importance of a disciple's inherent qualities in receiving a Guru's grace. Both the stone and the gem are polished on the same whetstone, which represents the Guru's efforts and teachings. However, the outcome is vastly different: the stone merely becomes smooth, while the gem transforms into a brilliant, sparkling jewel. This analogy implies that while the Guru provides the method for spiritual polishing, the disciple's own nature—specifically their capacity for 'strong faith at the Guru’s feet and the strength of courage which is patience'—determines their ability to absorb the teachings and truly shine. A disciple without these qualities is like the stone, unable to gain the luster of a true gem despite the Guru's work.