Can you explain the analogy of the stone and the gem being polished on a whetstone as it relates to a disciple's development?

The analogy in Chapter 19 of a stone and a gem being polished illustrates the role of a disciple's inherent qualities in their spiritual development. The whetstone represents the Guru's teachings and guidance, which are applied equally to all disciples. However, the outcome differs based on the disciple's nature. As the text explains, while the same process is applied, "the stone remains a stone, but the gem becomes a brilliant jewel." This suggests that even with a powerful Guru, the disciple's own capacity, represented by "strong faith at the Guru’s feet and the strength of courage which is patience," is what allows them to truly absorb the teachings and attain the brilliance of a gem.