Tielhard said:
My understanding of the situation is that under Constantine’s patronage an ‘authoritative’ Bible was assembled. The books chosen for inclusion were those which best supported the doctrines of the early church in Rome and the ideas Constantine wished to encourage. Many of the texts included were also edited at this time to better support then current doctrine. For example at least three Gospels were either completely omitted or were unavailable to the compilers, those of; Mary Magdalene, Thomas and Peter. As Thomas is made up of the teachings of Christ rather than a history of his life this has to be regarded as a serious omission.
MarkA says upthread that the first (Gnostic) compilation was c. 166, and the first Orthodox version not too much later. What I don't know is the state of play c. 300, just before Constantine got involved.
Undoubtedly there would be more variations than in OTL, and more circulation of books regarded as non-canonical by the orthodox. However ...
Tielhard said:
There will be no great councils and synods to argue points of doctrine and theology. Even if there are there will be no impetus for local congregations to accept their rulings.
Here I disagree. The tendency of Christian congregations to keep in touch with each other goes right back to Paul's letters, and there was already an emergent Catholic or Orthodox mainstream long before Constantine.
Even if Christianity had never become the state religion, or Emperors become directly involved in it, the days of persecution were certainly numbered, and the convening of councils would become that much easier. These councils would promulgate standard versions. Individual congregations might reject them, and whole regions might ultimately go their own way, but most of the Christian world was likely to coalesce around a standard Bible and probably a standard creed, more or less like the Nicene Creed.
Dark ages. This gets interesting. I don't know that the spread or form of Christianity has anything to do with the material factors that ended the Dark Ages. Barring lots of subtle butterflies (which, admittedly, are always possible), the moldboard plow will still spread, forests will be cut down, and the spur will allow heavy-armed lancers to deliver a powerful shock charge. In short, the factors that transformed northwestern Europe from a thinly settled frontier region into a densely populated and potentially powerful one.
So some form of suphisticated civilization is likely to arise in northern France, western Germany, and the Low Countries - the question is how much continuity it has with the classical past.
Monasticism was already around. The question, perhaps, is whether someone like Benedict of Nursia hits on the idea of "work is prayer," with the resulting impact on agriculture, copying of manuscripts, etc. Centralization is not needed for this, and in fact the early Benedictines were not centralized; each new foundation was independent. I'm not sure that Imperial involvement bears on this much, one way or the other - after all, the Empire in the west had already fallen to pieces before Benedict.
-- Rick