Can you summarize the reasons given in Chapter 4 for why saints incarnate, and what happens once their work is done?

Chapter 4 of Sai Satcharitra explains that saints descend to the mortal world when there is a decay of religion and people lose sight of their ultimate well-being. This happens when individuals become consumed by lust, hunger, and worldly pursuits like wealth and status, ignoring proper conduct. As this chapter describes, the saint's mission is to protect the system of castes and stages of life, destroy irreligion, uplift the distressed, and reawaken faith. Once their specific work is fulfilled and the mission is complete, they end their incarnation.