Can you describe the analogy of the stone and the gem and what it reveals about a disciple's development?

The source material in Chapter 19 presents an analogy to explain the development of a disciple. It compares the process to rubbing both a stone and a gem on a whetstone. While both undergo the same polishing process, their outcomes differ vastly: 'the stone remains a stone, but the gem becomes a brilliant jewel.' This suggests that while a Guru provides the same guidance and 'polishing' to all, the disciple's inherent nature and readiness play a crucial role. A disciple with the right potential, like a gem, will become brilliant. In contrast, another individual, like a stone, may become smooth but cannot gain the 'luster of a gem,' highlighting that the Guru's efforts are most effective on a disciple who possesses the necessary foundational qualities like faith and patience.