What does the story of the gem and the stone illustrate about the role of a disciple?

The analogy of the gem and the stone, found in Chapter 19, serves to illustrate the difference in how disciples respond to a Guru's guidance. The text explains that when a stone and a gem are both rubbed on a whetstone, the process is the same, but the outcome is vastly different. The gem becomes a "brilliant jewel" or a "sparkling diamond," while the stone merely becomes smooth. This metaphor suggests that the Guru's teachings (the whetstone) are offered to all, but only the disciple who possesses the inherent qualities of a 'gem'—implying qualities like faith and patience—can truly gain luster and transform. A disciple without these qualities, like the 'stone,' may undergo the process but will not achieve the same brilliant result, highlighting the importance of the disciple's own readiness and virtue.