Can you explain the metaphor about the River Ganges that's mentioned at the beginning of Chapter 47?

In Chapter 47, a powerful metaphor is used to illustrate the purifying power of saints. The text explains that the River Bhagirathi, or Ganges, washes the feet of the world and, in doing so, becomes soiled with accumulated impurities and sins. To wash away her own impurities, the river herself desires the dust from the feet of saints. The river is depicted as knowing for certain that there is no other way for her to be delivered from her sins. This analogy, presented in Chapter 47, powerfully elevates the status of saints like Sai, suggesting their grace is so immense that even a sacred entity like the Ganges seeks their presence for its own purification.