Can you explain the analogy of the gem and the stone in the context of a disciple's development?

The analogy of the gem and the stone, found in Chapter 19, illustrates the importance of a disciple's inner qualities. Both a stone and a gem are polished on the same whetstone, which represents the Guru's guidance and process. However, while the stone merely becomes smooth, the gem becomes a brilliant jewel. This shows that the Guru's efforts are the same for all, but the outcome depends on the disciple. A Guru expects "strong faith at the Guru’s feet and the strength of courage which is patience." A disciple with these qualities, like the gem, has the inherent potential to gain luster and brilliance through the Guru's polishing, while one without them, like the stone, cannot.