What was the purpose of Sai Baba's incarnation in Shirdi if he is the formless Brahman?

The text in Chapter 43 clearly states that Sai Baba's appearance in a physical form was an act of grace undertaken for a specific purpose. He manifested in Shirdi 'with the sole desire for the welfare of devotees' and 'for the sake of the devotees’ protection.' His physical presence was a response to the 'past merits of devotees.' Once his designated 'task for the devotees' was considered complete, he chose to leave the physical body. This implies that his incarnation was not a result of karmic necessity but a voluntary descent to guide and protect his followers, after which he returned to his 'previous unmanifest state.'