God is the same, yesterday, today, and tomorrow. Therefore, any discussion of Christianity must begin with a discussion of God. When people start to talk about the future of a group of people, they often forget the thing that unites those people. This is not to say that Christianity can't change, because it has changed, and it will continue to change. But, an analysis of Christianity should not forget the fact that God was, is, and shall be. It is difficult to look into the future because we are finite and fallible beings that often get prognostication absolutely wrong. So, in the spirit of guessing wrong, here are a few thoughts on the future of Christianity that will probably end up being wrong.
CHURCH
Of course, when we talk about Christianity, we typically end up talking about "the church", or as unbelievers call it "organized religion". The church has pretty much always been in flux. It has either been persecuted or chased. Or, it has grown in relative comfort, only to decline due to the apathy of society. One can find examples of all of these scenarios around the world today. In some countries, Christianity is spreading like wildfire, even in places where believers must meet in secret. Ironically, people have absolute freedom to attend church in the United States, but church attendance is declining in every state. It may be possible that the next 50 years sees a continued decline of "traditional" churches across America while at the same time "house" churches will spring up everywhere. Many will argue that the original church met in homes anyway.
PRACTICE
Christianity often comes under fire by the general public for its rigidity and intolerance. This may, over time, cause Christianity to loosen the tightness of certain theology in order to embrace a broader view of humanity. Of course, society itself can be rather fickle. We live in an age of ethical relativism that causes people to feel stifled by the requirements of organized religion. We may find I the future that society shifts back to wanting more structure in their lives, which may make Christianity more appealing again. The other thing that hopefully will happen over time is that Christians will figure out that they need to get out and show Christ's love a lot more, rather than huddling together behind closed doors.
I can't predict what will happen to Christianity in the future. None of us can. Only God knows, and He will reveal the future as He sees fit. For now, I will strive to just live each day and not worry about tomorrow.