Interesting…
First of all, I have to ask, why did you choose to not format this properly? I assume you know how, so you should just do it, for your own benefit and for the benefit of those of us that choose to read it.
I like the concept. As has been mentioned though, you don’t tell us their location within the church. I’m assuming they’re sat in the pews somewhere, but it’d be nice to know. Straight after INT. CHURCH – DAY (as your scene header should read), you should give us a description of the church. Is it a large church? Small? Is it in the town or the countryside? How’s it decorated? Paint a picture for us.
You don’t describe the characters either. Tell us what they look like, what they’re wearing, something very simple… The SINNER has greasy hair, his face is covered with stubble. He looks tired. Where does the pastor come from, you say he moves, but moves from where? What was he doing before hand?
For me, this needs more action. As it stands, it’s just a long list of dialogue. Describe for us what these people are doing as they are talking. Perhaps the pastor asks “What are your sins?”, the sinner then rubs his hands over his face, contemplating his sins, before replying “I killed a man.” A simple line of action like this helps us visualise it better. When you read this to yourself, you must be playing it out in your head, as if you were watching on a screen, yes? So what are they doing? Write that down!
All in all, though, I do think this is an idea worth running with, and the bones of your story are there. Just pad it out a little to help us (and yourself) visualise the whole thing a little better.
I look forward to seeing the next draft!