Is there something about Gnosis in the Ars Magica supplements ?
Especially on Sethians, Copts and Christians of Egypt ?
It seems the Gnosistics developed a kind of witchcraft melted with heretic christian religion (condemned in the Chalcedoine council in 451 AD).
So I think they are very close to the "Divine Magic" developed in "Realms Of Power - The Divine".
If "No", I'll try to create something from the supplements I know.
Or else, if you have some ideas from where I can start to investigate...
There are the Dark Gnostics, an Infernalist group described in "Realms of Power: The Infernal". As I reread the section, however, it also notes that some gnostic groups also qualify as Divine faiths (Catharism is given as an example).
I don't recall seeing much about eastern Christianity in any of the published 5E sources though...
The main distinction is that the Oriental Orthodox churches (such as the Copts) hold that, in Jesus Christ, the human and divine natures are fully merged together (though Jesus Christ does not have only one nature; that's a heresy), while Nicene Christians hold that he has both the human and the divine nature, separately. (If this sounds like incredibly arcane and technical theology to you, welcome to the club.) It's much more similar to the Nicene churches than it is to Gnosticism.
For Gnostics in general, I'd advocate Divine or Infernal Mystery Cults, depending on whether the particular brand of Gnosticism is corrupted by demons. In Western Christianity, Catharism is currently the main Divine Gnostic practice, and the Bogomils in the Transylvanian and Theban tribunals are similar (but less focused on ascetism).
As Ramidel says, the Oriental Orthodox Christianity is not Gnostic of course.
But, I was looking for documentation about the Sethians Gnostics and I tried to get a big picture of medieval Egypt and specialy how the local church percieve Gnosticism.
Divine or Satanic ?
1/ as they worship this mysterieous Baktiotha, they are Satanists (as I read in "RoP: The Infernal" -> thanks to Gremlin44).
2/ they invent spells about love, cure and exorcise evil spirits, it sounds Divine.
Being able to exorcise evil spirits and use "love" magic is entirely within the bounds of the Infernal. In general, canonically, the game tends to treat "free love" movements as Infernally-tainted. Furthermore, Sethianism says that eating the fruit of the tree of knowledge was a good thing; that's very much in line with Dark Gnosticism.
Valentinianism, Sethianism's brother movement, seems more Divine in character. (Both are apparently dead by 1220, though; how dead is up to you.)
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