I need help coming up with a way for the cleric to atone for his actions without making it a long drawn out thing. He is lvl 3. Details of what happened below.

I am running a demon heavy campaign and the first demon they run into is a dream demon. The group figures out it is a dream and used dream mechanics to help defeat this demon which would have been impossible otherwise. They wake one at a time to see a small demon before them injured with 1HP left. The demon offers a portion of the power he has collected over the years if they spare him. The ranger and rogue agree and choose their ability. The cleric, as expected, refuses and casts Guiding Bolt to finish the demon off. Before he finishes the spell I have an angel, who has been watching the entire time and would have stepped in if the party got wiped, descend crushing the demon and say that the has passed the trial.

The clerics response, I cast Guiding Bolt. I figured the cleric wanted the kill so I reword what happened and he said no I cast Guiding bolt at what I see.  I say the angle who's aura you can tell is a herald from the very god of light you serve? He says Yep. His logic is that he is a cleric and has already passed his trials and that the angel had no right to test him. In truth he wasn't the one being testing it was the other party members but he angel never got to explain that. The angel explained that it was his god that decided to make this a trial. The cleric didn't care and stated that by not helping he was no better than the demon.

At this point I was speechless. I had the angle just say "hmm" and fly away. I can in no way imagine a lawful good god not punish a cleric for this act of defiance/betrayal. He didn't want to specify what kind of god of light he served and only stated he is a Templar so I decided he is in the Church of the Silver Flame. Next session his god is going to revel that he is withholding all spells that can cause harm and he has disadvantage on all attack rolls until he atones for his transgressions. I was also going to have an evil force whisper into his ear saying to abandon his god and serve her instead. If he takes this offer he will have to change his Divine Domain, change his alignment to neutral and when called by this evil force he must do as told or he will die.

First of all, the unnamed evil force should not have the power to kill him if he disobeys. The most it can do is remove the power it grants him, send something to kill him, or kill him itself. A warlock's patron is a different thing entirely, but deities don't have the power to just kill any of their followers. They could, of course, grant the follower more power than usual, tearing them apart if they accept it, or they could warp the spells their follower casts in an attempt to kill them.

Anyhoo, atonement. The cleric shouldn't be able to do some crappy little task and then get away scot free. I would suggest having him take an oath of pacifism, never fighting unless attacked first, and even then he must fight blow for blow. If a creature attacks him once, he hits it back, and it runs, he must let it go. This shouldn't be a physical restriction at all. He is free to do anything he pleases, but if he breaks the oath, his power is revoked for good. If he ever complains about how it's unfair, remind him that he attacked a bloody angel. He should be lucky to be alive. If he says "Fine, I'll just worship another god of light," allow him to go ahead and do that. Doesn't mean he'll be granted powers. Gods can contact each other, after all. He could be placed on a sort of divine blacklist unless he atones.

A cleric gets all divine power from his/her god -- channel divinity, spells, etc. I would not allow any of that to work if he has angered his god. No spells, no channel D. None of it. He could atone... or switch to a new god (very hard to do, requires much RP, etc), or change to another class.

Atonement would be something difficult... Not sure what. I like the oath of pacifism suggested above.

Did you ask the player why they did this? Maybe they’re hoping for some kind of character arc from it you can help them with, or maybe just bored of the cleric and looking to make a big splash before they re-roll. I’d start there. 

This would be one of the times that the actual tenets of the faith and the deity's alignment becomes very important.  The Church of the Silver Flame was very Good and very against Evil.  The characters main mistake appears to be acting rashly and getting mad about being tested when they knew their faith was pure as the Silver Flame!  The cleric did not Trust the Silver Flame.

Loss of the spell casting abilities and turning would be immediate and highly appropriate.  I am torn on the disadvantage on attacks since that would hinder the party as a whole.  The cleric needs to be drawn into a story that expands how they did not Trust and need to learn the first tenet again.  Maybe use a quest like the Seven Samurai where they are pitted against hopeless odds to save the innocent.  The cleric would have to relearn the Trust in the Sacred Flame.  Depending on what actions they take, you could have several NPCs help give opportunities to repent.

I cheated and found the tenets online at: http://eberroncolumbus.*******.com/church-of-the-silver-flame

1. Trust in the Silver Flame. The Voice of the Silver Flame never lies. It will light your way to glory and salvation.
2. Heed the words of the Keeper. The Keeper of the Flame is your emissary. Through the Keeper, the Silver Flame speaks.
3. Fight evil in all its forms. Not everyone can have the strength or conviction of a paladin, but there are many ways to fight evil that don’t require one to draw a sword. We must also remain vigilant, for the one thing evil does well is hide in plain sight.
4. Lead a noble life, and encourage others to do the same. Temptations abound, but the wisest of us can recognize and avoid them. If you die with a pure spirit, you will be forever bound with the Silver Flame.
5. Share the faith. The Silver Flame can purify the darkest spirit. Share the power of the Flame with those who have not yet embraced it.

I think there just needs to be a discussion outside of the game to figure out what the PLAYER understands about his characters devotion to the Silver Flame. Does he understand his "rank" in the hierarchy compared to his God and an Angelic messenger of his God? Does humility have more merit than self-righteousness in his churches teachings? I think most players would enjoy that their God took personal interest in the group.

After you get this out of the way, I would move to game mechanics, provided the player still had interest in playing his character either in his God's service or otherwise.

When I said he will die I meant she would send an ancient black dragon after him or something similar.

I like the idea of an oath of pacifism or some similar specific restrictions on how he can use his powers.

I didn't ask him why he did that because it was after a 7hr game session.

Thanks for the link on the tenets I am sure they will come in handy.

Now that I have an idea of what to do I can call the player up and talk out the details and a story arc if that was his plan.

Thanks for your help.

Another idea: You could make a custom, very powerful, impossible-to-remove-by-Greater-Restoration, Curse that befalls the character. Then design some sort of complex series of services that must be performed to lift the curse.

If I were doing this, I would make it a multi-effect curse, with some act of service or atonement that lifts each effect one by one. So for example, maybe a black halo (reverse of an angelic one) hovers over the character's head, marking him as cursed, and while it exists, he has disadvantage on all charisma-based skill checks. Maybe his spell casting is completely gone. And he can't do Channel Divinity. That's 3 effects.

Then I would make 1 method of negating each of the effects. Maybe to get back Channel Divinity, he has to pray at the temple for so much time. Maybe to get rid of the dark halo he has to donate 10,000 gp to the poor. Etc. I'd probably make it take some time, so it might be several sessions during which the cleric is slowly removing one effect of the curse at a time, until he gets "back to normal."

I don't know BioWizard. None of that sounds very fun, even from an extreme roleplaying point of view where players thrive on interpersonal drama.

Still seems more like a flippant player disconnect rather than a game character issue.

I think you can make it very unfun.

from a logical stand point the cleric done bad and would be punished, logic may not be fun for you or your player. Not being able to use your toys not fun, having to play pious atonement not fun. For you, the PC and potentially the rest of the party.

so I would echo that you need to work with the player, why did they attack an angel. The justification is very arrogant, not a good cleric skill. From a narrative perspective I think there is a cool answer.

”What if the cleric is not who they say they are”

maybe they are actually trickery domain, maybe they are actually a warlock, maybe they feared the angel would reveal them, maybe they are actually a fallen Aasimar, maybe they gave a cursed weapon controlling actions.

talk to your player discuss options, but don’t go straight to “punish player, yourself and group” punishments are boring, secrets are fun

There are so many different ways this could be handled.

The fundamental issue here is communication. The player has one vision of how their character interacts with the world, their diety and the servants of their diety. The DM has a completely different view. The DM believes their view is correct and will punish the player until they make their character play the way the DM insists it must be played.

Anyone see the issue?

Resolving this requires an out of game chat between the DM and the player to agree on the relationship between the character and their diety. Clearly the cleric has followed the diety up to this point but a diety will have many followers. In this case the cleric disagrees with the actions of another follower of the diety (in this case some sort of angel). The angel watched and waited while a demon tried to destroy the minds of the character and his companions, then when the cleric was about to finish the demon this angel appears says you have passed the test and squashes the demon. Wut? From a role playing perspective, I could see the cleric being quite irate at some powerful follower of their diety sitting idly by doing nothing while the cleric and his friends experience significant risk and then just pop in at the end to say "good job". Do the followers of this diety have no respect or care for the people that worship the diety? Don't they feel responsible for those worshippers? What did this supposed "angel" think that they were doing?

So, in the moment of anger, the cleric casts a guiding bolt at this obviously misguided follower of their diety. How did this happen at all? If the angel is operating under the will of the diety then the spell could have either no effect or the cleric might even find his access to the magic blocked. The angel and the cleric could have a little discussion about what happened and why. The angel could even apologize if there is some reasonable justification for its actions. Keep in mind that guiding bolt, even it hits isn't going to do much of anything to the angel. The party can't defeat it and the player likely knows that so this is entirely a role playing exercise.

There are tons of ways that this could turn out ... requiring the cleric to "atone" is a punishment enforced by a DM intent on making the player/character conform to their vision of how the character should have reacted rather than trying to see the situation from the player/character perspective and role playing the interaction since the cleric is effectively powerless against the angel.

Anyway, the bottom line is the DM needs to talk to the player involved out of game and resolve the situation ... having the angel say "Ummm" fly away, do nothing and require the cleric to "atone" is not a resolution UNLESS the DM and player were already on the same page regarding the obligations of a cleric to their diety and other followers of that diety.

I have a cleric character that's giving up in her god too. Narratively, her power started to fade, and I included some hints as to why (a sentient weapon she has trouble attuning to). Mechanically, it's not very punishing to keep it fair. But the climax will be to present a choice: either find your faith again, or connect with this new diety. 

In her case, she's a wanderer, disciple of Marthammor Duin, who's tired of wondering. I'll be presenting the figure of Berronar Truesilver, goddess of home and family. She will pick to continue as a wanderer or to make her home where she is.

I don't know Eberon well, but maybe the Dark 6 is an good choice?

Player takes action, casts Guiding Bolt. One action. Player rolls attack. Player hits, demon dead. Player misses angel shows up. 

Angel would, in my game, need to have something to interrupt the player. Counter spell or something. 

Basically told there player they couldn't do what they wanted and railroaded the player with the angel. Thus possibly upsetting the player. Especially if the demon was going to die regardless. 

But it's your game so do whatever you want to do.