Could you explain the analogy of the stone and the gem that Baba uses to describe disciples?

The analogy of the stone and the gem, found in Chapter 19, illustrates the importance of a disciple's inner readiness and inherent qualities. Baba explains that even a powerful Guru expects a disciple to possess "strong faith at the Guru’s feet and the strength of courage which is patience." He compares the Guru's guidance to a whetstone that polishes both a common stone and a precious gem. While both undergo the same process, the gem becomes a brilliant jewel, whereas the stone only becomes smooth. This metaphor suggests that spiritual teachings affect disciples differently based on their innate capacity for faith and patience; only the disciple with the qualities of a 'gem' can achieve true, brilliant transformation.