C.S. Lewis’s BBC talks later collected as Mere Christianity were broadcast between 1941 and 1944. The talks were delivered during the Second World War and addressed basic Christian beliefs for a general British audience.
Lewis did not originally write one continuous book called Mere Christianity. The later volume assembled material from several broadcast series: The Case for Christianity, Christian Behaviour, and Beyond Personality. He revised the broadcasts for publication and combined them into the form widely read today.
The wartime setting helped make Lewis a prominent public religious voice, but the talks were not intended as a commentary on military events. Their focus was moral reasoning, Christian doctrine, and points of agreement among major Christian traditions. That history explains why the modern book has a layered structure.