What is the ultimate mission of a saint's incarnation, and what happens once that mission is complete?

The mission of saints, as detailed in Chapter 4, is to restore religious order and guide humanity. They work to protect the system of castes and stages of life, destroy irreligion, and protect the weak. Their task involves filling the foundation of Renunciation (Nivritti) to build the temple of Ultimate Truth, thereby uplifting devotees. They perform the work of religion and awaken faith in the populace. Chapter 4 clearly states that their incarnation is temporary and purpose-driven; once their specific work is fulfilled and their mission is accomplished, they conclude their incarnation.