I also always play the Norse in CK2. In fact, I've never played actual Christians in that game. I've also read the Edda and in particular find inspiration in the Havamal. However, I am neither Asatru nor a Christian. I am an atheist, small A. That means that I'm willing to look with clear and impartial eyes and say, truthfully, that Christianity really was a special religion, unlike any other.
Sigulbard wants to express something, but he doesn't quite get it right, perhaps because of a lingering dislike. Christianity was actually a multitude of heterodox teachings and gnostic mystery cults in the early days of the religion. It could be anything but a simple doctrine to get correct, as gnostics are often wont to craft needless complexity even in simple matters, simply to make themselves seem more enlightened than others. There would not be a standard and easily-followed orthodoxy for many centuries afterward, and the
sola fide shortcut to heaven through belief alone is actually a Protestant belief dating to no earlier than the 1500s! So, Sigulbard is quite out in his assumptions.
The fact of the matter is that Christianity was far more personal than the earlier religions. Yes, you didn't do elaborate rituals to propitiate the stern and distant gods looking down from unreachable heights. If you've read the Iliad, you've no doubt been struck by the way that the Gods banter and wager on the outcome of thousands of deaths around Troy. That was the distant notion of divinity in the ancient mind. Christianity brought the concept of a god that sacrificed for you, who fed the poor, defended women from being stoned, and ultimately suffered as humans suffered. You prayed to a God that had been a man to connect with his children. That's far different. It's revolutionary. By the 180s, when official persecution was still strong and on-going, it has been estimated that Christians were already 10% of Rome, though mostly the underclass.The faith largely spread among the poor and the women who had no other stake in society. I believe you'll find that Constantine was persuaded to moderation on Christianity through his mother being a Christian. Again and again in history, you'll find men being persuaded to accept Christianity because of influence from wives and mothers, including Saint Augustine himself.
So perhaps Christianity's time has passed now, but 1700 years ago, it was a vibrant young force. The ancient world was undergoing a cultural exhaustion that is evident in many areas of the arts, where nothing good or worthwhile survives in literature far past Tacitus, and the best poets of the age are poor imitators of Classical authors. It was a civilization in need of a new direction, and christianity filled that void. But there is no doubt that it was something new, and spread mostly by peaceful proselytization in the first three centuries. After Theodosius, around 400, it hardens and becomes a tool of the state with increasing orthodoxy and muscle. That happens to all social movements when authority claims them as a means to rule.
-Acceptance: Easier to trade/work/rule the remains of the Christian Roman Empire when you share the same faith, eh?
But... but... that implies that it's already
dominant!
The question was how it became dominant, not what happened afterward. How do you go from Christians being persecuted in Diocletian's reign, and we're talking serious persecution, to the Edict of Milan a few decades later, in which Constantine made Christianity equal to the Classical pagan beliefs? Much of this is reflexively saying, "Well, Christianity became dominant through its dominance."