Why did Kaka Mahajani's skeptical friend end up bowing to Sai Baba even though he promised he wouldn't?

Kaka Mahajani's friend, who was initially against idol worship, broke his vow not to bow due to a profound personal experience. According to Chapter 35, when the friend stepped into the mosque, Sai Baba spoke to him. The tone and vocal style Baba used was an exact, charming imitation of the friend's deceased father. Hearing what sounded like his father's voice coming from Baba completely amazed the man. The text states he "melted inside" and, forgetting his firm resolve, he bowed his head at Baba's feet. It was the personal and miraculous nature of the communication that overcame his skepticism.