Can you explain the metaphor about the River Ganges used in Chapter 47 to describe the power of saints?

Chapter 47 employs a powerful metaphor involving the River Bhagirathi, or Ganges, to illustrate the supreme purifying power of saints like Sai. The analogy posits that the Ganges, by washing the feet and sins of the world, becomes soiled herself with accumulated impurities. To achieve her own purification and deliverance from these sins, she yearns for the dust from the feet of saints. As Chapter 47 poetically describes, the river wonders, "When will the feet of saints touch me? When will they come to bathe within me?" This metaphor elevates saints to a status higher than even the holiest of rivers, suggesting their grace is the ultimate source of purification.