Christianity is in decline because the leaders and cultural institutions of predominantly Christian nations no longer promote Christianity (and instead, actively worked to undermine it). Islam is strong because the leaders and cultural institutions of predominantly Muslim countries actively promote Islam. It’s really as simple as that.
Christianity Will Survive, but only for the true believers who seek it out. In the past, calling yourself a Christian and going to church was like showing up for homeroom class. It was automatic, people didn’t think about it, they just did it. It was taken for granted that living the Christian Life was something that everyone should aspire to, even if many fell short of actually doing it.
But without that guidance and encouragement from political leaders, teachers, writers, artists, Etc, the flock loses its way.
How do you know when Satan takes over a town?
The streets are clean, everyone is polite, there’s no pornography, and the churches are full....where Christ is not preached.