What is the inherent nature and purpose of a saint's incarnation as described in the fourth chapter?

According to Chapter 4, saints are described as being naturally liberated souls who are always ready to uplift the distressed. Their incarnation is not for any personal reason but is purely for the sake of others, as they have no self-interest. Their mission is to protect the humble, poor, and weak, destroy irreligion, and awaken faith. They are said to fill the foundation of Renunciation (Nivritti) and build the temple of Ultimate Truth, thereby uplifting devotees. Once their specific work is fulfilled, they conclude their incarnation.