Can you summarize the vow Cholkar made and the personal sacrifice he undertook when he couldn't fulfill it immediately?

Certainly. According to Chapter 15, Cholkar's household was poor and his livelihood depended on passing an examination to make his job permanent. He made a firm resolve, vowing to Sai Baba that if he passed, he would travel to Shirdi and distribute sugar candy (khadisakhar) in Baba's name. Although his wish was granted, he faced financial hardship that delayed his trip. As a personal penance during this period of delay, Cholkar completely gave up sugar. The text highlights his commitment by stating that until his vow to visit Shirdi was fulfilled, he "avoided sugar as an inedible substance, And even drank his tea without sugar."