Lucifer's kinda like Christmas and Easter. A really cool story which resonates with pagans - because it was almost entirely taken from pagans - and incorporated into Christianity to convert pagans.
The Trinity's the same way. You have the vengeful god of war, death and authority (Odin), the valiant savior with ties to farming (Thor), and the nebulous spirit which watches over daily life. Then there's the eeevil antagonist who betrayed the others and tries to lead people astray, don't fall for his lies (Loki).
In this way the missionaries didn't have to convince people that their gods were false, just misunderstood. They were able to ease people in to monotheism by stages. The celebration of lengthening days becomes was always a celebration of the birth of Jesus (the farmer god). The Spring equinox celebrates the reincarnation of dormant flowers Jesus. They were actually worshiping Jesus all along, they just didn't know it yet.
Never mind that none of those inventions are based on scripture. The local people couldn't read Latin, only the clergy had that skill. Which is why a major part of the Reformation was the Church trying to stop the Bible from being translated... It *needed* to be kept secret, or people would question all the embellishments which made it palatable. Or so the Church feared.
Instead, hundreds of years later, Christians are desperately guarding co-opted pagan celebrations like Christmas as vital tenets of their faith. And blaming everything on Lucifer, or Satan the satyr goat-hooved carouser and troublemaker. They wildly overestimated how important the Bible was to actual Christians, compared to the traditions they invented.