The Christians and Catholics were not the main targets of the Nazis but were killed because they challenged Hitler's opinion. Five million Christian civilians were murdered out of 12 million total civilians kiled.
Hitler planned to replace the Christian religion with his own paganistic religion based on blood, war, and conquest. Hitler himself was trying to replace Christ as himself.
The Nazis were planning to replace the New Testament with a "Nazi Testament" of sorts, and totally eradicate the Old Testament.
