Based on Chapter 23, why do saints incarnate on earth, and why is it said to be difficult to judge their true nature?

Chapter 23 provides two key insights into this. Firstly, it explains that the incarnations of saints occur on earth out of benevolence, as a grace of the Almighty, specifically for the salvation of "dull-witted souls." The desire to even hear their stories is a sign of having merit (Punya) in store. Secondly, the chapter advises that one cannot understand a saint's true state by observing their external behaviors, such as their caste, conduct, or what they eat. Their essential nature is always beyond such superficial things, which makes them difficult to judge from an ordinary perspective.