I was prompted to ask this question by a discussion in another thread.
In 5e, can a player make a check to have his/her PC perform a miracle. For instance, if a fighter comes across a villager who is injured and dying, is it a valid action declaration to say "I pray for the villager's life"?
If the answer is yes, what is the relevant stat? WIS? And what is the DC? And what skill (if any) would grant a proficiency bonus to the check?
I wish it were possible for me to compose a short response to this, but I just don't see how its possible because it is (for myself) not a noncomplex question. There are several issues at play. I think I've written 3ish (?) posts elsewhere on the odd duck that is the noncombat action resolution system of 5e. You might have read them (or not).
First, I'm going to briefly look at how, and why, this exact thing would work (and is actually meant to be a part of play) within 3 codified conflict resolution systems. Systems where GM fiat (specifically GM fiat that isn't transparently expressed within the system via an agenda/principles paradigm) isn't deeply embedded into the architecture of mechanical resolution or the actual, impromptu codification of the form of resolution itself.
Dogs in the Vineyard
This sort of stuff is precisely what play is about and the system pushes play toward these thematic trials. The play procedure for the conflict resolution is:
(a) establish what is at stake,
(b) set the stage for the conflict,
(c) you take up your dice (this one would either by Acuity + Heart or Body + Heart depending on the specific circumstances...then you determine applicable Relationship/Trait/Belongings dice),
(d) the GM plays the antagonism (perhaps the mortal wound and the victim's failing body...perhaps the person's loss of will to live...perhaps a demon trying to claim the life and then the soul of the victim in question) and takes up relevant dice,
(e) you take turns Seeing and Raising until the win/loss condition is met (very roughly, its much more complex than that including Giving early and Escalating)
The fiction and its fallout is spat out of this process. The GM's job is to play the antagonism to the hilt, effectively narrate the dramatic ebb and flow of the conflict as it unwinds and then concludes, resolve the stakes (based on the former), frame the follow-up conflicts. And Fallout is handled.
Sounds pretty familiar, right? Depending on what the antagonism was (a would-be mortal wound or a demon) + the relationship of the Dog to the mortally wounded (plus other fictional variables that we can't know because we aren't playing!), the fiction would change dramatically based on (1) the ebb and flow of the conflict during play procedures and (2) the ultimate resolution of the conflict's stakes.
But rituals, ceremonies, miracles, gun-fights, confronting the sins of the mortal soul and possibly the hidden supernatural behind them....that is what the game is about and the thematics, the GMing ethos, and the system's mechanics push play toward it.
Dungeon World and
D&D 4e
These systems' conflict resolution are extremely similar from a GMing ethos perspective and a play procedure perspective. They are both fiction-first. They're both about dramatic resolution of thematic stakes. The only thing that is different is the machinery of the conflict resolution. Machinery-wise, what they do share though is (a) system-codified difficulty (the subjective DCs of the Skill Challenge framework and the Basic Resolution mechanic for all conflicts in DW) and (b) system-established win/loss conditions of the conflict and its stakes whereby the GM is obliged to incorporate into the fiction.
In 4e, in such a conflict as you've devised above, a player might appeal to whatever god to take on the physical suffering/burden of the victim. They may roll a primary Endurance or Con check for this and it might move things forward positively, set things back, or close out the scene (with a win or a loss). The same thing might occur in DW. Or it might happen with Religion (a direct invocation to the god for intercession). There are a lot of possibilities. We'd set the stakes, frame the scene, grab the dice and find out what happens.
They may not seem it to outsiders, but they're actually extremely similar to Dogs in all ways (save the finer subtleties of the machinery...which do have their own impact on play).
D&D 5e
After a thorough examination, I'm convinced that the GM's job in 5e noncombat action resolution is extremely "fiatish." I'm certain this was the intent of the designers. "Rulings not rules" is basically a rallying cry for heavy-handed GMing and a system that requires it.
Unlike the other systems above, the GM decides everything in a procedure something like this:
Can this even be tried (who knows - this is intentionally left to the table) >
What is the difficulty of the task (a process-sim evaluation) >
What exactly is the impromptu established "win/loss condition (mechanically)" >
What is going to be the machinery of resolution itself (eg one check, stepped checks, contest, fail-forward, etc) >
What am I now obliged (if anything) to incorporate into the fiction?
There are so many areas where the GM is expected to interpret, ad-lib through the system's fuzziness/lack of hard guidance and hard infrastructure, and make judgement calls.
Procedurally in 5e, what exactly is the process-sim basis for the Medicine DC with respect to the appeal to the god in question? The gravity of the wound or debilitation? The victim's or responder's piety or ties to the god? Do we mash that together? I don't have any clue and I certainly wouldn't want to be at the controls of that. GM fiat.
What is the win/loss condition? Success on one check...two checks...three checks (without a failure in between?) and the fiction is closed out? What if they fail? There is strict advice to fail-forward in 5e. But when? How much? When is the scene closed out and the stakes negatively resolved with a campaign loss? All GM fiat.
Further, as can be seen in this thread (and many, many others), there are all kinds of off-the-cuff play procedures that GM would be devising at the table in-situ to resolve this. And others that say flatly "no way dude...take that crap elsewhere." This is, of course, a feature for folks who want loose, open design which mandates heavy-handed GMing (as storyteller) as the glue.
TLDR; I don't have the slightest clue whether a Medicine check can be made for a miracle. I'm inclined towards "no" but lucky for me I don't have to make that decision!
EDIT - Accidentally cut/paste a paragraph into the wrong-subheading. Fixed.