Why was the son in the Tarkhad family so worried about going to Shirdi, and what promise did his father have to make to convince him?

The son's hesitation stemmed from his devout daily routine of worship. As Chapter 9 details, he would not consume any food without first taking a bath and offering 'Naivedya' (food offering) to a photograph of Sai Baba. His primary worry was that if he left for Shirdi, this regular worship would be interrupted. He was especially concerned because his father, Babasaheb Tarkhad, was a follower of the Prarthana Samaj and not accustomed to idol worship. To alleviate his son's anxiety, the father promised to take over the responsibility. He gave his word, stating, "Without first dedicating to Sai, no one will consume food," and assured his son he would offer Naivedya daily. This solemn promise is what finally convinced the son to undertake the journey to Shirdi.