The source describes Nana using road clay as Udi. What does this incident suggest about the role of faith versus the physical substance in receiving Sai Baba's grace?

The incident in Chapter 33 where Nana Chandorkar uses a pinch of clay from the road as Udi provides a profound insight. His wife's severe fever subsided the very moment he applied the clay after offering a prayer to Sai. This strongly suggests that the miraculous power did not reside in the physical substance of the Udi itself, but rather in the devotee's unwavering faith and the sincerity of the prayer directed towards Sai. The clay merely acted as a conduit for this powerful faith. This event highlights a key principle: sincere belief and devotion are the true catalysts for receiving Baba's grace, making the physical medium secondary.