In the late Roman Empire most people were poor. The state was in the hands of a hugely wealthy elite who called all the shots. The logic for a religion was inevitable. The only source of converts was to appeal to people in poverty. The only source of cash was the government. The winning formula turned out to be highly centralised Christianity. This combined stuff that would appeal to the broke who stood to inherit the Earth if sufficiently meek while guaranteeing that that which was due to Caesar would actually be rendered unto Caesar. Anything that convenient had to be true. It was also worth wiping out any competition. So we ended up with Christian monoculture.
In a sense the fact that it was Christianity that triumphed rather than some other form is simply a detail. The winner was always going to share the same properties. For example, any dominant religion was going to take over existing festivals like the ones in winter and spring and retcon them to the new framework. So the spring festival gets the passion of Christ allocated to it. Of course it keeps some pagan elements. Eggs and bunnies don’t feature in the gospel. And Easter is the name of a Saxon goddess, though sadly that is all we know about her.
But unfortunately, there is a limit to how plastic even something as flexible as a religion is. If you are using the death and resurrection of Christ as your narrative it has a bit of a drawback for a four day festival. The story is that he was nailed up on the Friday and came back again on the following Monday. This leaves an inconvenient lack of action over the weekend. Sunday is a day of worship anyway, so you can soup that up a bit. But what do you do with Saturday?
I suppose they could have called it Still Dead Saturday or something. It would sound a bit better in latin as Mortus Tamen. But in the event nothing was done with it, so we end up with a normal weekend Saturday in the middle of Easter. I always think that this is a blot on an otherwise rather splendid festival. In the top half of the northern hemisphere were I live, it usually falls around the time the weather improves and the days get longer. It really is a great time for a bit of celebration. And who doesn’t appreciate an excuse to eat buns and chocolate. It’s just a shame that it will now forever be associated with a story that is both rather gruesome and which has an unfortunate hiatus in the middle.