What does the author say about the qualities of a powerful spiritual story at the beginning of Chapter 21?

At the start of Chapter 21, the author reflects on the intended impact of spiritual narration. He suggests that a speaker's words are in vain if they do not deeply move the listener. According to his description, a truly effective spiritual story should cause the listener to sway, the hair on their body to stand on end, their throat to choke up with emotion, and tears of love and joy to flow from their eyes. He considers any narration that fails to delight the listener and evoke such a profound emotional and physical response to be futile. This sets a standard for the captivating and transformative power of the stories about Sai Baba that he is about to tell.