If you are a paid Christian: a 'minister' or 'pastor', that is, the reflexive answer is often "I'm a minister (which could be confused with a being a member of the government), or, I'm a pastor.
In most cases, a conversation stopper. I suppose you could continue. 'And I'll bet you have no idea what my typical day brings.' That might ignite a conversation.
A better way is one I've used. It's easy to give a title: can sound pompous, and can be a conversation stopper. So I describe, briefly, what I do (e.g.' I help organizations improve their capability').
If I were a paid Christian, I'd describe my work, making it a conversation opener:
- I'm a community facilitator/educator/worker...
- I help people learn about personal growth
- I'm a kind of personal coach; I help people work out their life goals
- I help people have conversations about life
- I help people deal with life, etc.
- I help people live forever.