RoP:D (p.48) states that Holy Methods and Powers do not face the same restrictions in terms of duration that Hermetic Magic does, and in particular that they can achieve "permanent" durations without vis or rituals at the cost of 4 extra magnitudes being added to the base effect (the same cost as D:Year). But what does "permanent" exactly mean in this context? Does it mean permanent as in "of indefinite duration" or as in "the magic is gone in an instant, but a natural effect stays behind permanently"? It seems fairly clear from the examples that for healing powers the second meaning is the intended one, but what about e.g. a Blessing that grants the Inspirational Virtue "permanently"?
I've always assumed the latter given the sample spells and in light of it likely being easier to just write up a "Permanent" guideline rather than using a comparatively awkward +4 Magnitudes.
As for the suggested effect, "Grace" Duration could be a good option. Also, "The Church" establishes that my mystical societates have access to the ability to initiate people into their Mysteries.
When I wrote it, I intended that benefit for momentary Ritual-level effects only. Healing, creation, Characteristic boosts, that sort of thing. Permanently granting new Virtues would be too powerful, I think.
Ah, I see. This sentence clears up almost all of my doubts, thanks! Almost: can transformations such as those achievable through Intervention (e.g. changing a statue into an animal) be made permanent?
If God wills it, I cannot see why not. I would use that duration as the SG's bitch: it can be permanent in the sense as "permanently magical" or permanent as in "ritual instant" depending on circumstances. It can easily switch between the 2 formats as well.
I wouldn't allow it myself, but YMMV. I think it's more true to the setting if the Intervention-type miraculous effects are always temporary, like other Muto effects. There are special Durations that can make an effect nearly permanent, of course.
Thanks for all the answers, everyone!