What was the specific promise Babasaheb Tarkhad made to his son before his son left for Shirdi, and what was the son's main concern?

The son's primary concern about traveling to Shirdi with his mother was that the daily worship and Naivedya (food offering) to Sai Baba's photograph would not be performed regularly at home. Chapter 9 highlights his worry, stating he didn't trust his father, a follower of the Prarthana Samaj, to properly handle the idol worship. To alleviate this, the son made his father promise, saying, "Without offering Naivedya to Sai, no one should consume food at home." Babasaheb Tarkhad accepted this condition, giving his word of assurance and telling his son to go in peace, which finally convinced the boy to make the journey.