What is the meaning behind the analogies of the mother tortoise and the gem versus the stone that Baba uses?

In Chapter 19, Sai Baba uses powerful analogies to explain the subtle nature of a Guru's grace and a disciple's development. The analogy of the mother tortoise, who is on one riverbank while her young are on the other, illustrates how a Guru can nurture and protect a disciple through a loving gaze alone, without physical proximity or verbal instruction. This shows that the Guru's grace transcends conventional teaching methods. The analogy of the gem and the stone clarifies that while the same process—serving a Guru—is applied to all, the outcome depends on the disciple's inherent qualities. A disciple with strong faith and patience is like a gem that becomes a brilliant jewel when polished, whereas another without these qualities remains a stone, merely smoothed by the process but unchanged in its essential nature.