Thus the ‘decline of religion’ becomes a very ambiguous phenomenon. 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 or (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. It should be added that this new freedom was partly caused by the very conditions which it revealed. If the various anti-clerical and anti-theistic forces at work in the nineteenth century had had to attack a solid phalanx of radical Christians the story might have been different. But mere ‘religion’ — ‘morality tinged with emotion’, ‘what a man does with his solitude’, ‘the religion of all good men’ — has little power of resistance. It is not good at saying No.
The decline of ‘religion’, thus understood, seems to me in some ways a blessing. At the very worst it makes the issue clear. To the modern undergraduate Christianity is, at least, one of the intellectual options. It is, so to speak, on the agenda: it can be discussed, and a conversion may follow. I can remember times when this was much more difficult. ‘Religion’ (as distinct from Christianity) was too vague to be discussed (‘too sacred to be lightly mentioned’) and so mixed up with sentiment and good form as to be one of the embarrassing subjects. If it had to be spoken of, it was spoken of in a hushed, medical voice. Something of the shame of the Cross is, and ought to be, irremovable. But the merely social and sentimental embarrassment is gone. The fog of ‘religion’ has lifted.
— C. S. Lewis, “The Decline of Religion” (in God in the Dock)