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

The analogy of the stone and the gem, found in Chapter 19, illustrates the crucial role of a disciple's inner qualities in their spiritual progress. The Guru's teaching is the 'whetstone' that polishes both the stone and the gem. While both undergo the same process, the outcome is vastly different: the gem becomes a 'brilliant jewel,' while the stone merely becomes smooth. This metaphor suggests that the Guru provides the same guidance and opportunity to all, but the disciple's receptivity and inherent nature—specifically their capacity for Faith and Patience—determine the result. A disciple without these core virtues, like the stone, cannot gain the spiritual luster of a true gem, even under the guidance of a powerful Guru.