How does Sai Baba use the 'tortoise-vision' analogy to illustrate the power of meditation and a Guru's grace?

In Chapter 19, Sai Baba uses a powerful analogy to explain how his grace works, comparing it to a mother tortoise. He explains that the tortoise can be on one bank of a river while her young are on the other, yet she nourishes them with her gaze alone, without providing milk or warmth. The young ones simply need to meditate on their mother. Baba refers to this as 'tortoise-vision' (Kurma-drishti). This illustrates that by constantly meditating on the Guru's form, a devotee can receive all necessary spiritual nourishment and grace, leading to the ultimate goal, just as the tortoise's children are sustained by her loving sight.