If I murder you, that is a sin. Once upon a time no one would argue with the death penalty being appropriate. Now things have changed. The murderer is sick and needs understanding. Think what a traumatic experience it was to commit a murder! Poor lamb, they say. And lawyers like Clive Stafford Smith suggest that since a life has already been lost, it is not worth spoiling another too - namely that of the murderer.
This shifting in the "cultural norm" of morality (not God's law, which is unchanging, but the perception of what is generally agreed amongst people) dictates the stories we can tell. Think of the most recent adaptation of Murder on the Orient Express. It's a simple story: a child was brutally killed and the murderer got away with it. Everyone who loved the child boards the same train as the killer and they murder him. In the original story, Poirot is sympathetic and holds the truth of the death a secret. It might be rough justice, but it is justice nonetheless and if the police cannot fathom who did it, he will not tell them.
In the new version, it is more complicated because the child-murderer is penitent. Poirot undergoes a lot of soul searching. It's agony. And it brings the viewer to the same modern idea surrounding murderers: should their lives be ruined for what they have done? This version of the story fails because Christie never asked such a question in her life. The strength of her mysteries is dedication to truth and devotion to justice. They were Christian qualities. Without credible Christian principles in the context of real life, such virtues will disappear from art too.
One may come to feel that a culture which lacks a firm centre of coherent life-giving wisdom, a common sensibility or sophia as distinct from institutions, scholasticism, and debate, is no culture at all, and that the post-Christian world is essentially cultureless.
The Pelican Guide to English Literature 6: From Dickens to Hardy, ed. by Boris Ford, p.56