Or, I guess more importantly, they're tricking you into establishing a secular conversation with this guy before he springs a bunch of Bible thumping on you.
I recall having some church youth group knock on my dorm door in college and start with the question "Do you believe in fate?" Right away I knew I was in for the next 20 minutes of lecture and continued questions about what I believe in. I've been hiding from door to door evangelists ever since.