What are the effects of Papal Interdiction in game beyond the real world? When Pope Clemantine III issued an interdiction on Pisa for refusing to join the Tuscan league, did that strip away the divine aura until it was lifted? Lower it? Temper it (if so in what temper?)
From my understanding, a local interdict, i.e. interdict placed on an area, as implied by the name is the prohibition to celebrate sacred rites (e.g. mass, confession, batpism) in that place. This has by itself supernatural consequences in Ars Magica mechanics, from declining Auras, to fewer faith points available to the "average christian", to said christians remaining in a state of sin (which makes it easier for demons to do their stuff etc.). I would not really add anything else. Of course, if the church authorities also want to, say, temper the local Divine Aura appropriately, they can do so, but it's not an automatic effect of the interdict.
Wikipedia notes that "local interdicts were almost entirely suspended on five feasts of the year: Christmas Day, Easter Sunday, Pentecost, Corpus Christi and the feast of the Assumption of Mary. Besides, in the case of a general local interdict, it remained permissible to celebrate in the cathedral or the only church in a town, but without any solemnity such as the ringing of bells and the playing of music, Mass, baptism, confession, and marriage."
Pope Celestine III (en.wikipedia.org/wiki/Pope_Innocent_III ) in early 1198.
Standard handling of such an interdict in ArM5 is described in Rop:TD p.76 lower box Interdiction, which also states
Given that the specific interdict you ask about did last some 2 months, its effects on the ArM5 Divine might have been quickly recovered.
If I remember the discussion of Infernal Auras properly from RoP:I, lands subject to papal interdict have all Infernal Auras rise in strength by 1.
I feel that the effects of an interdiction would be opposed to its intent, which is fo bring back the population on "the right path".
Intent of correction and effect of correction are often at odds.
From the Church's point of view, you are being denied something you deeply want, forgiveness, and threatened with horrible punishment after death.
From the interdicted point of view, it's not necessarily that directly bad, and you don't have moralizers telling you what a rotten sinner you are for going about your ordinary life.
The Divine angels and saints must suffer the knowledge that sinners are being denied the path to salvation.
To demons, it's playtime!
... Similarities to the modern credit system, interestingly enough ...
This is how I perceive it also.
That one made me laugh...