You have asked: what a Christian is to do?
I get the sense that unless they are narrow-minded Bible-thumpers, and oblivious to the world around them, Christians are as disoriented as everybody else in a civilization that has been losing its common ground.
For me, a good metaphor for the binding power of any viable cultural/theological/moral belief system is the image of innumerable iron filings thrown upon a table.At first, they all lie in different directions, disconnected from each other. But, as soon as you put a Big Magnet under the table, they all immediately align and point in the same direction – toward a common center. A common deep culture – cultural/theological/moral, operates just like such a Big Magnet on the hearts and minds of all the people.But the Big Magnet of western civilization, under attack for so long now, has been losing its pulling power. So, sensing this, and fearing the dangers of moral and cultural fragmentation, the political class invented the idea of putting hundreds of smaller magnets under the table, hoping they would have the same pulling power as one Big Magnet.But immediately, with no common pull, the people turned in hundreds of different directions, each group hewing unto it’s own kind.It was a good try, and faced with the fact that, as the poet Yeats wrote, “the center cannot hold,” any one of us might have proposed this as a desperate last-ditch unifying strategy.All we have is lots of smaller magnets under the table now, and the de-centering this causes in the public mind is likely a natural and predictable stage on the way down. There’s a lot of hopeful, if often fake rejoicing in our differences.But everyone knows there is no Big Magnet any longer, and there will not likely be one again in our lifetime.