That's really the only rule. Anything that relates would help. But, i would prefer not to write it on the usual: Calvin, Luther, reformation, etc.
it has to be about 8 pages.
any intriguing topic you can come up with would be awesome.

I'm stuck. ha ha
very fascinating ideas so far! they're so original. thanks so much :]
theist: i didn't ask for a thesis. i asked for a topic... so uh.... don't judge me.
George: good idea but I'm agnostic.

more details: surprisingly, the professor said anything at all relating to or inspired by a topic in protestantism is perfectly fine. he wants us to venture into interesting topics i think and not what we've covered in class which was Luther, Henry VII, reformation, Calvin, etc.
so yep, any ideas at all are perfectly fine