The idea of a "purpose of life" is a hard one to let go of for a lot of people raised within a religion.
That's part of the deal with a religion, right? It answers that "Why are we here? Why are we alive?" We are here because a God made us, he has told us why. Which sort of implies we're here to serve him.
Because why would you make something that doesn't benefit you in some way?
But, here's the thing. There is no grand orchestrating idea. There is no answer to Why?
There is no purpose to life. Well, other than what you give it.
You get to pick the why.