Could you explain the analogy of the River Bhagirathi (Ganges) as it is described in Chapter 47?

In Chapter 47, a powerful analogy is used involving the River Bhagirathi, also known as the Ganges. The text explains that while the holy river washes the feet of the world and purifies others, it becomes soiled itself from the accumulated impurities. To wash away its own sins and impurities, the river desires the dust from the feet of saints. This metaphor powerfully illustrates the supreme purifying power of saints like Sai Baba, suggesting that their holiness surpasses even that of the sacred Ganges, which itself seeks them out for its own deliverance.