What specifically caused Kaka Mahajani's friend to break his promise and bow to Sai Baba?

The friend of Kaka Mahajani, who was a devotee of the formless and against idol worship, had made a firm resolve not to bow to Sai Baba. The pivotal moment that caused him to break this promise is detailed in Chapter 35. As he set foot in the mosque, Baba addressed him with the words, "Why have you come, sir." The friend was instantly astonished, not by the words themselves, but by the tone. The text states that the charming tone was a "perfect imitation of his father's exact vocal style." Hearing speech as if from his deceased father's mouth caused the friend to melt inside, forget his previous resolve entirely, and bow his head at Baba's feet.