What is the purpose of the incarnation of Great Souls like Sai Baba, and what happens when their 'task is over'?

According to the insights in Chapter 43, the rise of Great Souls has the 'welfare of people as its purpose.' They incarnate by their own will, filled with devotion, with the sole desire for the well-being and protection of their devotees. These avatars, being personifications of the form of Brahman, are not subject to the normal cycles of birth and death. When their specific task is completed, they do not die but 'join their true form and merge into the unmanifest.' For Sai Baba, this meant transcending his physical body of 'three and a half cubits' to become one with Brahman, filling the entire world and continuing to enjoy his true self while remaining present in the hearts of his devotees.