Can you explain the lesson Baba taught the woman who wanted to fast, as described in Chapter 32?

In Chapter 32, a story is recounted about a woman who wished to observe a strict three-day fast upon visiting Sai Baba. However, Baba thwarted her plan. He had her make puranpolis and then ensured she ate them to her heart's content. The purpose of this act, as explained in Chapter 32, was to impart a deeper spiritual lesson. Baba taught her that "wearing out the body for others' sake - this blessed act is true welfare." Through this experience, he made her understand that selfless action holds more virtue than ascetic practices like fasting, a lesson she would never forget.