Can you summarize the story of Cholkar and the vow he made to Sai Baba?

Certainly. Cholkar was a man from a poor household whose job security depended on passing an examination. As described in Chapter 15, he made a vow to Sai Baba that if he passed, he would travel to Shirdi and distribute sugar candy. His wish was granted, but due to financial constraints, which are metaphorically called the 'threshold-ghat,' he was unable to fulfill his vow immediately. During this delay, he completely abstained from sugar, even drinking his tea without it. When he eventually reached Shirdi and fulfilled his promise, Baba demonstrated his omniscience by telling another devotee, Jog, to serve Cholkar tea that was 'well-filled with sugar.' This act revealed to Cholkar that Baba knew of his secret vow and personal sacrifice, which brought tears of joy to his eyes and solidified his faith.