Original: Sri Sai Baba and His Teachings by Acharya Ekkirala Bharadwaja is an in-depth study of Sai Baba's life routine and activities. B.V. Narasimhaswamiji has written important books such as Sri Sai Baba's Charters and Sayings and Devotee's Experiences of Sai Baba.
Simplified: Sai Baba can be realized only through faith, he will be with you always, when you need someone hand to hold think of Sai Baba sayings "Why fear when i'm here".