The book is written by the disciple of Sri Atmanand. He has grown up under the shade of his mentor. He says, Sri Atmanand was not a mentor in the usual sense of the word. Author then goes on expounding the teachings of his master.
The teachings of the master are no different from ADVAITA (NON-DUALITY).
The best thing I liked about this book is that it teaches you about non-duality from three dimensions, which are actually three different states of mind. Waking Dreaming Deep Sleep