What accounts for the survival and global spread of Christianity?
That's a good question to ask, I think, and I may have a fairly simple answer. Let's look at what I think may have led to all of that and have a discussion about it:
Religion seems to be a natural development of pretty much every human culture and society. Religions seem to have developed in keeping with the knowledge and social structures of each culture and society. Some cultures created naturalistic deities to reflect the puzzling thing that is the world we live in. Animals, heavenly bodies, and even mountains, oceans and rivers have attained deity in one culture another another.
Multiple deities with their own responsibilities are pretty common, too. Some religions that survive today have hundreds or even thousands of deities. That's complicated, really, and hard to keep straight, really. Heck in Greek and Roman religions, the deities even fought with each other and sometimes came down and mated with humans to create demi-gods. They all seem to have human characteristics, naturally enough, I guess.
And names. Lots of names. Names that have become days of the week and months in our Western languages. More confusion. How is it possible to keep track of all of that? But, it was important that deities be like humans in some ways. They needed to be like humans, since humans appear to have created them. We need to be able to identify with our deities, see.
All was confusion, until some clever fellow in some culture came up with the idea that One deity was enough, as long as that One was omni-everything. That simplified the situation considerably, and became pretty popular, at least in some places and in some cultures. Just One name to remember who did it all and that's that.
Having a single deity was very convenient and provided an easy explanation for all sorts of stuff people didn't understand. How was the universe created? Well, Poof! The One wished it into existence and there it was. One deity is very useful in explaining stuff to the curious monkeys humans are without causing too much confusion.
And rules. People need rules. So if the One dictates the rules, then fear of what the One might do was a good way to keep things more or less peaceful. And Worship. Deities require worship to keep people conscious of the rules and to have a way to plead for better conditions when things get tough. So, clever people figured that all out and wrote down rules that were pretty much the same everywhere humans lived in groups, large and small.
People die, too, so they want to know what happens when they die. We'll, it's easy to use that to help with that rules stuff. If you follow all the rules, see, and worship like you're supposed to, then good things happen to you after you die. If you don't, though, it's bad. VERY BAD! So, be good. But humans have a really hard time being good, it seems. They get angry, avaricious, lazy, etc. So, it's really impossible to be good enough, and that's bad.
Christianity handles all of that nonsense right away. All you have to do to get those posthumous rewards is to believe. If you believe, the bad stuff gets erased-like and won't keep you from getting good stuff when you die. There was this sacrifice by the son sent down, who is also the father, and some other stuff, or something. It's pretty mysterious, but that doesn't matter. You just have to believe, worship from time to time, and do your best to behave and the rewards are yours.
It's a perfect shortcut. You don't have a whole pantheon of deities to appease and worship. Just One, who is really three at the same time, but never mind. And you don't have to be perfect, because that's impossible. All you have to do is believe that you'll be forgiven when you screw up and everything's good. What a great concept! So much simpler. So much easier to deal with. There's still some worshiping to do, of course, some rules you're supposed to follow, and stuff like that, but if you screw up, remember that you believe in the One, so it's all good. You're home free.
But you do have to believe, see. If you don't, then what happens after you die is bad. REAL BAD! It's easier if you believe, so what makes the most sense? Why not believe? Why take chances with your afterlife? And so, as the story spread, people thought to themselves: Say! This is way easier than how it is in my religion. I'm going to switch to worshiping the One. It's easy to believe in that. The rules are about the same, anyhow, and I've never been able to follow all those rules, so if believing makes it OK if I screw up, I'm in!
And so, Christianity spread like wildfire through Western Civilization and then out into other parts of the planet. What's not to like, after all, about a simple religion that gives you a shortcut solution to getting out of that BAD stuff that might happen when you die?
Does that make sense?
Sorry about all the words and stuff. It's complicated, see...
= new reply since forum marked as read
Pretty straight forward i would have thought??? 
