Can you explain the metaphor about the River Ganges that is used at the beginning of Chapter 47?

At the start of Chapter 47, a powerful metaphor is used involving the River Ganges (Bhagirathi) to illustrate the supreme purity of saints. The text explains that while the Ganges washes the sins of the world, she becomes soiled herself with these accumulated impurities. To achieve her own purification, the river desires the dust from the feet of saints. Chapter 47 describes the river thinking, "When will the feet of saints touch me? When will they come to bathe within me?" This metaphor elevates saints like Sai Baba to a status higher than even the holiest of rivers, implying their grace is the ultimate source of purification.