What is Sai's fundamental teaching on overcoming the fear of death?

The core teaching is that death is the great fear of worldly existence, and the way to become fearless is to hold firmly to the Guru’s pair of feet. As detailed in Chapter 37, the Guru grants a non-dual intellect, which is crucial because fear enters wherever there is an obsession with duality. By surrendering to the Satguru with your body, speech, mind, and intellect, all talk of the fear of worldly existence ceases, as the Guru is the one who removes everything and grants the place of fearlessness.