@WanderingCurious,
Motivations may differ, some see it as a life or soul saving work, others see it as a continuation of their religious leaders ministry. Some just like to tell people about something that is important to them or makes them feel good.
Faith is a powerful motivator, and what it motivates people to do will differ from religion to religion.
It is also worth noting that everyone perceives the world through their own eyes bound by their own biases, and each one has a model of their universe according to their own understanding. This will often differ greatly even amongst those of the same religion, that is what makes humans interesting. Unfortunately too many people think their model of the universe is the only one worth considering