Can you explain the analogy of the stone and the gem from Chapter 19 and its significance in the context of a disciple's development?

The analogy of the stone and the gem in Chapter 19 illustrates the importance of a disciple's inherent qualities and readiness for a Guru's teachings. The text explains that when a stone and a gem are both polished on a whetstone, the process is the same, but the results differ vastly. The gem 'becomes a brilliant jewel,' while the stone 'remains smooth by its own nature.' This signifies that a Guru's grace and instruction (the polishing) are available to all, but the disciple's transformation depends on their inner potential. As Chapter 19 states, a Guru expects 'strong faith at the Guru’s feet and the strength of courage which is patience.' A disciple possessing these virtues, like the gem, can achieve spiritual brilliance, whereas one without them will not gain the same luster, regardless of the Guru's power.