The question that often stops Christians in their tracks.
This might play out in such questions as, innocently asked, 'why do you go to church? ...read the Bible, believe in Christ/Christianity, believe in God...' or even 'do you think/believe that I'll go to hell?' and the correlated one about God of love and evil being present.
Be ready with some answers, their rebuttals and your responses.
The easiest on is the one about hell. The answer is: only if you want to.
OK, here are the others:
Why do you go to church: I want to learn how to live forever.
Why do you believe in Christ/Christianity: So I can live forever.
Why do you read the Bible: it's the story of who we are, the story of reality.
These are all 'first step' answers. They are designed to invite discussion and without having to make long speeches.
Or, you might like these answers:
Why do you go to church: I want to connect with others who want to really enjoy life.
Why do you believe in Christ/Christianity: he shows the way of the story of life/it gives the best understanding there is of life and its future. [oh, have you examined all of them? No, because Jesus of Nazareth rose from the dead, I'm happy to follow him.]
Why do you read the Bible: it's the best picture of reality there is and it meshes with life that we experience at every point, but it also shows the way to live forever.
Again, first step answers that can lead to a chain of conversations.