What is the purpose of the analogy involving the River Bhagirathi (Ganges) at the beginning of Chapter 47?

In Chapter 47, the River Bhagirathi, or Ganges, is used as a powerful metaphor to highlight the supreme purifying power of saints. The text explains that the river becomes soiled by washing away the sins of the world and, in turn, desires the dust from the feet of saints to wash away her own accumulated impurities. This analogy serves to elevate the holiness of saints like Sai, suggesting their grace is the ultimate source of purification, even for a sacred river that purifies others.