I think it was Dietrich Bonhoeffer who coined the term "secular Christianity", or at least popularised it in one of his "Letters from Prison", while he was awaiting execution for involvement in a plot against Adolf Hitler.
God in the center: Bonhoeffer on our religionless culture
He was in prison, in a country under siege by the US and British bombing fleets (he often heard the bombers arriving), the Russians in the East, and the Allies in the West. Death was so common that apparently hardly anyone feared it any more. And of course what might be called organised religion in Germany had almost fallen by the wayside.
At the same time Mankind had become increasingly self confident. Planes were flying hundreds of miles to drop tonnes of bombs, the atomic bomb and nuclear power were just around the corner, V-2's and V-1's were still hitting London from time to time, antibiotics had been invented and had saved a lot of lives, the jet engine had arrived and the computer had been invented.
In another 25 years, Mankind would land on the moon, a quarter of a century after the most destructive war in history.
Fast forward another 50 years, and Mankind is even more confident. There might be setbacks, but the show goes on on. As a consequence a lot of our young people think they can live without God. Add the contraceptive pill (and incidentally I think it should have been approved for married couples as recommended by two committees set up and enlarged by two Popes), and the sexual revolution, and it is very easy to ignore the church's teaching on contraception and sexual ethics.
In my own peculiar world view, I think God intends to drive us off the planet, and I think the incredibly accelerated development of technology points towards this looming scenario. If so, the idea of churches and cathedrals (and mosques and synagogues) will probably become a thing of the past, as it will be difficult enough just to survive in a very unfriendly environment, leaving little capital left over for extraneous purposes.
What will "religion" mean then?
Which pushes us right back to what Bonhoeffer was trying to say about "religion-less Christianity', where God is at the centre of life, and not at the periphery, not a deux-ex-machina when we have reached the end of our tether, and we fall back on Him in desperation as our sole way of deliverance. The writer of the linked article used HG Wells "War of the Worlds" as an example of a "deux-ex-machina" where Wells pulls in a bacterial infection as the reason for the Martians eventual defeat. Very handy, and it arrived just in time. But how often does God act like that?
Bonhoeffer could see it coming. I don't think he had the answer to it, and was executed before he could continue. But at least he alerted us to be aware of it, and to start doing some serious thinking about "religionless Christianity". Because it's coming, and it won't be much point complaining we weren't warned. The writing is on the wall.
The hiatus before the storm hits is all over the West.