Why would Sai Baba need someone else to be a 'pretext' to write his own story? If he has the power to do it himself, why not just manifest the book directly?

According to the account in Chapter 2, the process of writing the book is a means of spiritual development for the devotee. Sai Baba states, 'He is merely a pretext; I myself shall write my own story!' This is conditioned on the devotee's surrender: 'He should dissolve his ego and surrender it at my feet. To one who acts thus in life, I give full assistance.' The act of hearing, reflecting, and writing becomes a spiritual practice. As Chapter 2 explains, the work 'is accomplished by the One to whom it belongs; he (the author) is only made a pretext.' This method allows the divine to work through the devotee, fulfilling the devotee's wish while also serving as a lesson in dissolving the ego.