A guilt-ridden priest with a dark secret finds himself held hostage in a Catholic confessional by a sinister, unseen terrorist wearing a suicide vest strapped with explosives.

Simultaneously provides too much information and not enough.

"Guilt-ridden priest" is enough to define your protagonist - don't tell us here he has a secret; reveal it in the story. Also if he's feeling that guilty, a dark secret is implied.

No one "finds" themselves doing something. It's weak wording, makes your character passive. If he's held hostage, just say he's held hostage, then give us an idea what he's going to do about it. That makes him active.

You already told us he's a priest in a confessional; why specify Catholic? Isn't that a given? If not, does it matter? Maybe in the story, but not here. Get rid of any extraneous words.

Being a terrorist already defines the antagonist as such; no need to describe such a person as sinister. He's a bad guy, we get it. Also no need to tell us the guy's unseen, because it brings up too many questions: if he's unseen, how do we know he's a terrorist or what he's wearing? Surely the script itself can answer these, but no need to raise them here. Just tell us who, what, and why. Leave the intricate details for later.

More unnecessary words: suicide vest. "Strapped with explosives" pretty much tells us everything.

Cutting all this down leaves you with "A guilt-ridden priest is held hostage in a confessional by a terrorist strapped with explosives." Succinct, but this is what I mean by not enough information. You've told us who and what, now we need to know why. You've given us the protagonist, antagonist, and the stakes, but what's the conflict? Sure, one guy's threatening to blow up the other guy, who probably doesn't want this to happen, but what's the real reason for all this? What's caused the confrontation? Why this priest, why here, why now? Is it related to his guilt, his secret? Surely it must be, but you have to give us a taste to make the story compelling.

As an example, without knowing the actual story: "A guilt-ridden priest is held hostage in a confessional by a terrorist strapped with explosives who claims to be his long lost son." You can't just tell us who's in the story and what it's about; you have to tell us why it's a story.

Possible title: Confession?

I think this has potential and is very timely,
Here is how I think your story could work out.
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1: You set up the priest as 'respectable' make him look like a good guy, show him saving the cat. (First 5 to 10 minutes tops, no more than that)

2: He goes into the confessional (Page 10) and the terrorist is on the other side with his bomb. (Inciting incident)

3: The terrorist says he is going to blow up the church because of the child abuse scandal

4: The priest then tries to talk the terrorist down. He uses his skills as a priest. (This is the meat of the story)

5: As the conversation continues, the terrorist gets more and more specific, he knows things about the priests personally

6: However, the priest, talking about God and forgiveness?seems to actually convince the bomber to give up his plan.

7: Then the bomber hits the priest with the twist. "You are the one who did the abuse! You abused me!" (The turn into the third act)

8: The bomber didn't pick this priest at random, he is the bombers personal abuser, when the bomber was a child.

9: The priest denies it, but the bomber is relentless

10: Finally (The Irony) The priest confesses.

11: The priest pleads the bomber for forgiveness

12: The bomber tells the priest, "Ask God for forgiveness when you see him"

The bomb explodes: The End (Fade to black)
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The idea behind this would be; when the movie begins the priest is the 'good guy' and the Terrorist/bomber is the 'bad guy' however once the third act hits, we see it is the opposite, the situation has turned. The priest is the bad guy and the bomber was his victim when he was just a kid.