What is the primary motivation for a saint's incarnation, and what is their ultimate mission as described in Chapter 4?

As explained in Chapter 4, the incarnation of a saint is a selfless act, undertaken purely for the benefit of others. The text states that saints themselves are naturally liberated, but they descend to Earth to uplift the distressed and have no self-interest in their actions. Their mission is to protect the humble and the poor, destroy irreligion, and reawaken faith. They work to fill the foundation of Renunciation (Nivritti), build the temple of Ultimate Truth, and easily uplift devotees. Once their specific work is fulfilled, they end their incarnation.