What is the meaning of the analogy of the stone and the gem being polished on a whetstone as explained in Chapter 19?

The analogy of the stone and the gem, as presented in Chapter 19, illustrates the role of a disciple's inherent quality in their spiritual development. The text explains that even if a powerful Guru provides the same teaching (the whetstone) to all, the outcome differs based on the disciple. Both a stone and a gem are polished by the same process, but "the stone remains a stone, but the gem becomes a brilliant jewel." This signifies that while the Guru's guidance is essential, the disciple must possess the necessary inner virtues—specifically "strong faith at the Guru’s feet and the strength of courage which is patience"—to truly absorb the teachings and achieve brilliance.