The future of Christianity must be looked at from both a secular and an eternal standpoint. Obviously, eternity is forever and is assured, as long as one believes that Jesus Christ died for one's sins and rose again from the dead. Recently I read a very apt description of our life's journey a Christian knows his eventual destination, but must trust God to get him there, much like an earthly father driving his child to school: the child is not concerned with the method of transportation or the route because he trusts his father to get him there safely.
Christianity in the world is under attack and has been for some time. Typically, and for years, the news reports show martyrdom and cruelty and terror directed at Christians worldwide. However, only recently have Christians in the US come under personal attack.
There are arguments about separation of church and state, disagreements about the religious proclivities of the founding fathers, discussions about using the Bible in public schools, prayer in schools, the wording of the Pledge of Allegiance, and so forth. Why? Because a minority of individuals in this country are upset that their "rights" are being trounced upon. A minority, by definition, means that fewer people are protesting, not more, and that is certainly not how a democracy works.
Why should the many cater to the whims of the few? Only God can answer that. Is this a test of mankind? It appears to be. At least a test of Christians in the US.
Politicians are supposed to listen to their constituents; all of them, yes, but it seems that in a democracy they should listen more closely to the majority of voters, not the vocal few. Perhaps it's because those few are indeed more vocal? Perhaps Christians need to step up, and stand up for God.
If churches stopped preaching that everyone is "okay", if they stopped bowing to those who persist in sin with no repentance and those who claim the Bible is changeable and fallible, if they stopped trying to "fit in" with society by opening coffee shops and replacing altars with stages then, Christianity in the modern world may stand a chance.
The future of Christianity does indeed look bleak; this downward spiral of morality and increasing tolerance for any and all, despite wrongdoing and wrong-thinking. Yes, there is right and wrong, black and white everything is not a shade of gray. The individual must be tolerated, but his sometimes depraved and immoral beliefs must not be accepted.
Christians must speak out for their beliefs, and stand up for God, regardless of consequences. It is a very hard thing to do. The Bible says, "...be in the world, but not of the world...." This is what we must do. Speak for change, speak for God, speak for the truth. Our lives here are but a journey, it does not matter what happens to us here because our destination is assured.