Can you explain the concept that 'death is a characteristic of the soul's nature' and how it relates to realized beings like Sai Baba?

The source material presents a complex view on mortality. Chapter 43 states that death is attached to birth and is a characteristic of the soul's nature, while life is seen as a modification of the body. For ordinary beings, this is an inseparable cycle. However, for great souls who 'place their feet on the head of Time,' this cycle is irrelevant. Sai Baba, being the complete Supreme Brahman for whom the world is an illusion, is beyond such concepts. He incarnated for the welfare of devotees and could leave his body at will, burning it in the fire of Yoga to merge back into the unmanifest.