Explain the metaphor of the gem and the stone as it is used in Chapter 19 to illustrate the relationship between a Guru and a disciple.

The analogy of the gem and the stone in Chapter 19 serves to explain why disciples progress differently under the same Guru. The text notes that both a stone and a gem are polished by the same process on a whetstone, just as a Guru provides the same teachings to all. However, their inherent nature dictates the outcome. The gem, possessing innate quality, "becomes a brilliant jewel," while the stone "remains smooth by its own nature." This metaphor, as explained in Chapter 19, illustrates that while a Guru's guidance is essential, the disciple's own inherent wisdom, faith, and capacity for patience ultimately determine their ability to absorb the teachings and achieve spiritual brilliance.