According to Chapter 30, what is the ultimate spiritual boon granted by Sai's grace, and what is the devotee's prerequisite to receive it?

Chapter 30 describes the ultimate boon of Sai Baba's grace as something far beyond material gain. It states that one upon whom grace is bestowed "attains inconceivable great power." This power is explicitly defined as spiritual wisdom: "The wealth of discrimination between Self and non-Self - all knowledge is attained." The prerequisite for the devotee is unwavering faith and complete trust. The chapter illustrates this by describing how devotees, "craving for Sai's spoken words, become entranced" and hold onto His every word with absolute faith. It is this complete surrender and trust that stills the wavering mind and makes the devotee receptive to the highest knowledge that Sai's grace imparts.