According to this text, why do great souls like Sai Baba even bother taking a human form? What's their main purpose?

Chapter 43 clearly states that the incarnation of great souls like Sai Baba is motivated by a single, profound purpose: the welfare and protection of devotees. The text specifies that they take various avatars 'with the sole desire for the welfare of devotees.' He appeared in Shirdi, drawn by the accumulated merits and devotion of his followers, specifically 'for the sake of the devotees’ protection.' Chapter 43 further clarifies that 'The rise of such Great Souls has the welfare of people as its purpose.' They are not bound by the physical form they inhabit, which is merely a vessel to carry out their mission of helping and guiding humanity before they merge back into their unmanifest true form.