Post-Christian: What does that mean?

We discussed how we live in a post-Christian world; a world where Christianity and it's moralistic views or traits are not considered commonplace. Some say it disappeared when secular Nationalism took over, and everyone turned to idolizing their country and it's own greatness. Now, in this day and age, Christians talk of being outside the norm, and being apart from the world, saying we're separate as if it is a bad thing. It's talked of as if it's something to regret.

When Jesus was killed, it wasn't as if only the Christian faith was the only one around. There's been a diversity of faith for lifetimes. So why do we consider our time to be the one of post-Christianity? If we are truly not of this world, and we are supposed to be the few, isn’t it a little narcissistic to think that we’re the last of a dying breed, as if we’re somehow more special than the people that came before us?

I mean sure, a perfect world would be one where we can all share the same views and morals and live in peace. There's a word for that: utopia. But, didn't God say that there could be no utopia on earth? Isn't heaven supposed to be that dream we hold out for during our lives? It’s a little confusing to me how we’re an outlier when we’ve been called to be one for generations before this.