Why did Baba take a physical form in Shirdi if he is an eternal being beyond birth and death?

The source material provides a clear purpose for his incarnation. Chapter 43 states that Baba appeared in Shirdi with the 'sole desire for the welfare of devotees' and for 'the sake of the devotees’ protection.' His manifestation was not a random birth but a willed event, prompted by the 'past merits of devotees.' He took a physical form to complete a specific task for his followers. Once that 'task for the devotees is over,' he chose to leave the body and merge back into his unmanifest state. This shows that his physical presence was a compassionate act undertaken for the salvation and benefit of those devoted to him.