Based on Chapter 4 of the Sai Satcharitra, what are the primary reasons for a saint's incarnation on Earth?

According to Chapter 4, saints incarnate on Earth during times of significant moral and religious decay. This happens when people lose sight of the ultimate goal (Paramartha) and become obsessed with worldly sources of happiness like wealth, status, and family. The text explains that saints descend to protect the system of castes and stages of life, destroy irreligion, and protect the humble, poor, and weak. Their incarnation is described as being purely for the sake of others, as they themselves are already liberated and have no self-interest.