I don't get the part about the tea. Why was it such a big deal when Baba told Jog to give Cholkar tea with sugar?

The instruction about the tea was a profound moment because it was Sai Baba's way of showing his omniscience and confirming his acceptance of Cholkar's devotion. As detailed in Chapter 15, Cholkar had secretly given up sugar as a personal penance during the long period he was too poor to fulfill his vow of distributing sugar candy in Shirdi. When he finally arrived and completed his vow, Baba told his host, Jog, to "Give him cups of tea, well-filled with sugar." This specific instruction stunned Cholkar, bringing tears to his eyes, because it was proof that Baba knew about his secret sacrifice. Baba, who didn't even drink tea himself, said this to explicitly signal to Cholkar that his vow and his hidden penance were both seen and accepted.