Why did Sai Baba's Guru not give him a secret mantra, and how did Baba explain this teaching method?

Sai Baba explains in Chapter 19 that despite his intense desire, his Guru never gave him an "ear-mantra" or secret instruction. To illustrate how the Guru's grace works without such formal methods, Baba uses the analogy of a mother tortoise. He says, "The mother tortoise is on one bank of the river, the young are on the other sandbank; she nurtures them through sight; the effort of a mantra is useless." Just as the tortoise feeds her young with her loving glance alone, Baba's Guru protected and nurtured him with his merciful gaze, even from a distance. This demonstrates a form of teaching where the Guru's grace and constant protection are conveyed through focused attention and love, rendering a spoken mantra unnecessary.