Using the analogy of the stone and the gem from Chapter 19, explain the role of a Guru in a disciple's development.

The analogy of the stone and the gem, found in Chapter 19, illustrates the transformative but selective power of a Guru's guidance. Just as a whetstone polishes both a stone and a gem, a Guru's teachings are applied to all disciples. However, the outcome depends on the inherent nature of the disciple. The text explains that while the same process is used, a stone will only become smooth by its own nature, but a gem becomes a brilliant, sparkling jewel. This suggests that while a Guru provides the means for spiritual polishing, the disciple's own quality, faith, and receptiveness ultimately determine their potential for spiritual brilliance.