Something that's been running through my mind while reading this discussion is the notion that the Divine provides vis for magi to use. I'm not sure it's that simple. Vis is a Magic concept: it's something that creatures aligned with the Magic realm use. The Divine doesn't need vis; it works with other sorts of power, like Divine Might or what the rules call Faith Points. Many characters can use this power like vis, but by doing so they may be abusing it. Like everything else, there's always the argument that if the Divine wanted magi to use the essence of a divine beast with their magic, it would have made it less risky.
I was kind of assuming the Vis hadnt come from slaying the host of the Lord, now thats just begging for big trouble.
And if Gawd had intended men to fly, he wouldn't have invented the railroad.
Uh, yes and no.
In much the same way that crime is a concept of law enforcement, I guess. The two are certainly connected, yet that doesn't mean that crime is somehow connected only to law enforcement.
(Meh, the analogy is weak at its surface. The point is that you're mixing cause and effect, how someone interacts with or defines something vs what it "is".)
Just because magi can make use of it, and clergy cannot (as a rule), doesn't negate the premise that it is Divinely given, or at least inspired. There are divine Auras, and clergy don't care about them - but that doesn't mean that those auras aren't tied directly to the big G.
You're right in that the Divine doesn't need vis - not the big G, not holy agents, not mortal clergy. Yet, there it is, markedly different from "magical vis", the same way that Infernal vis is different.
So - what's the diff? I'd suggest "something", and since all we have is Infernal vis and Auras to use as a pattern, well, there ya go.
My point was that there's characters who could legitimately make that argument in the setting, that since the power of the Divine is dangerous to incorporate into most magic, the Divine does not like magi doing that.
If there were no magi in Mythic Europe, would vis still exist? The raw supernatural power would be there, but I'm suggesting that the concept of vis would be meaningless because no one would be saving it up or using it for things other than worship of the Divine. What magi call vis (it could be argued in the setting) is not Divinely given, since it is not necessarily intended to be used in that way.
Hermetic magic can target the Divine, like using a ReVi spell to control an angel. Leaving aside whether or not that's a good idea, the spell is clearly Magic in origin, though it affects something that is Divine. Likewise, magic that makes use of the raw power of the Divine realm, or divine vis, is still aligned with the Magic realm. From that, I argue that vis is a Magic concept.
Though, hmm... a holy character with Invocation can use vis to improve his chances when performing a miraculous effect. This may be the influence of the Magic realm on divine powers, though, like how Holy Magic is the influence of the Divine realm on magic powers.
You don't think clergy care about Divine auras? I think they should. Many of the ways they make use of Divine power work better in such places. Miracles are more common, for example. Divine powers are more potent. Although I guess most clergy don't have holy powers. Still, they want bigger churches, right? They make pilgrimages to sacred sites?
Well, yes, it's true that there is vis associated with the Infernal realm, and infernalists can use it, though they need a special Virtue to do so. However, I would think magi would be especially anxious to distinguish their concept of vis from an infernal concept of vis, since the use of vis is one of the ways that Magic has more sympathy with the Infernal than the Divine. 
But is divine vis markedly different from magic vis? Is infernal vis? I mean, you use it the same way, it's just riskier when you botch. It doesn't align your magic with the Divine or the Infernal or anything like that. It can have weird side effects, of course, but very little of that is definite, apart from the three different kinds of infernal vis. I'd say it is quite similar, in fact-- as similar as three supernatural wolves, each one aligned to a different realm. They're all wolves, and when they die their remains can be used for many different things; the pelts for making furs, for example. Likewise, the supernatural power invested in the different carcasses can be used by magi to perform their magic.
Yes, but there wouldn't be as many botches with it!
"Intended"? You know the "intention" of The One Who Created Vis, the Big G? wow, I'm impressed!
(Who is intended to win the Superbowl this year?) 
I suggest that if this were "Ars Divinica", you'd be making the opposite argument for parallel reasons. The rules focus on magical uses that Mages make of vis, because this game is about Mages and Magic, not about Clergy and... Clergic... stuff.
Further, there exists in Mythic Europe a longstanding Order that has, in large part, dedicated centuries of research to finding uses for this vis, in a relatively organized and coordinated way. The church may have such researchers, but not on the same scope - it's just not part of their doctrine.
I would suggest that there are many other uses of divine vis for clergy, we, as Players, just don't know, nor much care, about them.
I would suggest, that given the Medieval paradigm, and the nature of legend & divinity, that the following might be true on the use of Divine Vis:
If Infernally tainted vis corrupts as a side-effect, indeed as its central intended effect no matter what it's used for, then Divine vis should purify, heal, and restore hope. Divine vis should do this as a not-always intended effect, one that perhaps even overshadows the intended effect.
That it could only be used by the pure of heart, or at least only used with a purity of intent, or by a repentant caster.
That an object used with this vis will appear not to work until given the right circumstances and/or wielder.
That it if it is used for selfish purposes, it remains completely inert, allowing for its potential goodness to continue, but not wasting itself on the small-minded goals of humans or magi. It might even have the subtle effect of not only making the spell fail, but of attracting exactly the sort of events or effects that cause the caster to repent.
That it may be interpret intentions like a holy opposite of the "Djinn's boon" syndrome. (Where a Djinn will grant your wish to the letter but violate your intent, the Divine vis will grant your wish to the letter but do so in some unintended way that might be counter to your intention, but fulfill the Divine's goals.) This might be true, even if it violates the limits of (hermetic) magic.
... the scrying spell worked perfectly! Anything heard or seen by his ghostly minions was known to him! But so was their suffering; even long after the spell should have ended, their cries of pain and loneliness echoed in his head, colored his dreams, clouded his vision. He wiped his eyes with a sleeve already soaked with tears of remorse, and contemplated how to release this next spirit from its servitude...
That it would oppose the Infernal, like a beacon of holy light might cut through the miasma of a cursed regio. Divine vis used to oppose the Infernal does so in some sort of inspirational, plot-furthering, even spectacular way, purifying the world, at least partially, of such influences.
... and the stone amulet shone with such holy light that the spirits in that dark place could not approach ...
If it were my Saga, I would have Divine-tainted vis cause pain or banishment to Faerie. This might be lenient on my part, but seems in keeping with the myth.
Of course, the best answer is usually the one that makes the Story more interesting. To have it sort of "disappear" because the mage tried to misuse it is not very interesting.
Following on Meddwyn's thought-- what if Divine vis is a sort of reverse trap for magi, in that it's purpose is to help them approach the concept of a pious magus and understand that such a thing is possible...that the spirit of the Divine is not so divorced from the Magic?
Sometimes it seems like the Divine is set as an opponent (or at the very least a hinderance) to magi; couldn't this just as easily be a sort of message sent in the form that magi are most likely to handle and receive?
-Ben.
I imagine that anything with enough Divine power that magi could use it as vis would probably have a Faith Point in it; i.e. it would be a relic. Perhaps magi can harvest vis from relics and other holy things, but looking at it this way sort of emphasizes why this is such a risky proposition.
When I talk about the motivations of the Divine, it is always in terms of speculation, and usually from the perspective of those in the setting, because the Divine is one of the great unanswered mysteries of the canon. So of course I would never say I speak for the Divine. Also, while it often seems that the Divine is often an antagonist in my stories, I feel I try to understand the perspective of those who serve it, and to most of them I think it's a "for-them-or-against-them" situation. When you throw in with the Divine you're on their team, and otherwise you're not.
It is possible that vis-relics are some sort of test or challenge for magi, and that their ability to use the power of the Divine with their magic is intended to convince them to follow a more righteous path. I like the idea of a holy magus who believes this, and who extracts vis from the Dominion and distributes it for this very purpose. I imagine most other magi wouldn't appreciate this very much, though, because you're so much more likely to go into Twilight if you botch, not to mention all of the other side effects the storyguide can slip in.
AMAZING IDEA Erik!!! 
I love this relic vis!
Xavi
I've always assumed that Vis, like Might, represents the power of creation, tainted by whichever realm it is associated with. Thus Infernal Ignem Vis is the potential for fire twisted to hurt, Magical Ignem Vis is the potential directed towards burning, Divine Ignem Vis is twisted towards illuminating and Faerie Ignem Vis is twisted towards dancing and shifting. All of these being the figurative, rather than literal things, of course.
Vis is just the manifestation of the power and potential of being, and everything uses and refines and shapes it. It's not solely magical, nor is it solely the property of magi - the Order just happens to use more of it than most.
As for how to handle it in Sagas, I'd treat it exactly as Infernal Vis (which does, I admit, have some minor rules associated with it), in that it works just the same but has some additional, minor effects which make the story interesting. And, indeed, the same for Faerie Vis. As for using Divine vis to cast a spell to commit a sin, I think that having a minor angel show up or some miracle to happen to intervene is not only appropriate to the setting but also fun.
Perhaps this is an oversight in the rules as written.
Now that this discussion has us thinking about the subject, it makes sense to me that a Divine Aura would enhance Presence & Communication rolls for priests during their ceremonies. Perhaps it could also be a positive modifier to study totals of Church Lore or Divine Realm Lore.
Magi get an aura bonus to their Lab Totals; so why not clergy?
And, to stretch even further...
The Dominion deals not just with the clergy and issues of divinity, but of Christian society as a whole. Why couldn't a divine aura have some "game" effect on all the believers that exist within that aura?
This would be a strong reason why so many Christian folks in Mythic Europe are willing to spend time and effort building churches/cathedrals, and attending ceremonies there. They actually feel the benefit!
-DC
Saints, angels and those alligned with dominion for thier powers would get a bonus, but mankind, in his state of 'free-will' isnt by default aligned to any of these particular powers. Although he may live his life essentially Christian, unless he makes those extraordinary steps towards the divine, he remains essentially a 'floating voter'. Hence, no particular effect from any realm.
The parish priest is generally a thousand miles away from from true insight into the nature of God, and he too, lacks any particularly strong alignment. It is an essential part of the nature of the divine which means only a very small number of people truly appreciate it in this mortal life and manifest its powers. Such is the grace and will of God.
For my games it works best to keep the divine as univolved as possible because one thing which is abundantly clear is that the will of God transcends all rules and thats the kind of power players would rather keep a distance from. On the plus side, the divine tends to be much more low-key than other realms other han the auras generated by its followers.
RoP:tD : Tempered auras