What is the meaning of the analogy comparing a stone and a gem being polished?

The analogy of the stone and the gem, found in Chapter 19, illustrates the importance of a disciple's inner qualities in spiritual development. The text explains that both a stone and a gem are polished by the same process on a whetstone. However, the outcome is vastly different: "the stone remains a stone, but the gem becomes a brilliant jewel." This suggests that while a Guru provides the same guidance and 'polishing' process to all, the disciple's inherent nature and spiritual readiness determine the result. A person without the innate qualities of faith and patience, like a stone, may become smooth but cannot gain the brilliance of a gem. A true disciple, like a gem, possesses these qualities and can therefore be transformed into a "sparkling diamond" through the Guru's grace.