What is the metaphysical explanation for why saints like Sai Baba are considered untouched by birth and death?

From a metaphysical standpoint, as detailed in Chapter 43, saints like Sai Baba are not subject to the cycle of birth and death because they are identified with the 'complete Supreme Brahman.' For one who realizes the truth of Brahman, the world itself is an illusion, and therefore, consciousness of the body is non-existent. The text states that birth and death are false imaginations, arising from the union and separation of the body and senses. Enlightened beings, who incarnate by their own will for the welfare of devotees, have already 'killed death' and placed their 'feet on the head of Time.' Their physical form is merely an adjunct, and its departure is a voluntary act, like merging into the unmanifest, not a cessation of being.