Here’s something C. S. Lewis wrote in a 1946 essay called “The Decline of Religion”:

The `decline of religion’ so often lamented (or welcomed) is held to be shown by empty chapels [in the Oxbridge colleges]. Now it is quite true that that chapels which were full in 1900 are empty in 1946. But this change was not gradual. It occurred at the precise moment when chapel ceased to be compulsory. It was not in fact a decline; it was a precipice. The sixty men who had come because chapel was a little later than ‘rollers’ (its only alternative) came no more; the five Christians remained. The withdrawal of compulsion did not create a new religious situation, but only revealed the situation which had long existed. And this is typical of the ‘decline in religion’ all over England.

I think it’s pretty obvious that the situation that obtained at Oxford and Cambridge when chapel attendance was made optional is closely analogous to the religious situation in America today. Everywhere in America, and even in the deep South, being a Christian has ceased is rapidly ceasing to be socially rewarding or even acceptable.* More from Lewis:

One way of putting the truth would be that the religion which has declined was not Christianity. It was a vague Theism with a strong and virile ethical code, which, far from standing over against the ‘World’, was absorbed into the whole fabric of English institutions and sentiment and therefore demanded church-going as (at best) a part of loyalty and good manners as (at worst) a proof of respectability. Hence a social pressure, like the withdrawal of the compulsion, did not create a new situation. The new freedom first allowed accurate observations to be made. When no man goes to church except because he seeks Christ the number of actual believers can at last be discovered.

That’s what we are discovering. The question is whether American churches will have the intellectual and spiritual integrity necessary to recognize and accept how completely they have relied on the social appeal of a “vague Theism” and how little they have spoken to those who go to church because they seek Christ. What’s at stake here is merely life or death.

*I changed that on reflection — where I live in central Texas, and in the many parts of the Southeast, being known to have a church community is still an index of trustworthiness in some business and social contexts.