Well there's an easy answer to that one. See, Christianity is true and the very best lies are spiced with bit of the truth so as to trick even the most intelligent (a gift from God BTW) into refusing said truth and condoning their own damnation (the only way that actually happens as well BTW).
The "true" parts were acknowledged and the false parts were discarded. Said pagan faiths intuitively got they were missing something. They had the concept of a "hidden" god. A god they knew somehow existed yet their pantheon didn't acknowledge nor offer an avenue of worship. A popular statement from the earliest evangelists was that they represented that hidden god. That got their foot in the door. After that well, as they say, the rest is history. There is a damn good reason the pagans dropped Thor/Odin/etc. for the true faith and the one true God and his son Jesus Christ.
It's happening at a great clip in the "East" as we speak fun fact. By around 2040 China's gonna be a "Christian Nation" full stop. As in, there will be at that time so many ardent followers of Christ that the Communist Party will get booted out much as Queen Isabella booted out the heathens/heretics/unbelievers from Spain upon the conclusion of the Reconquista.
Despite what many may say, I state again why it was a good and most merciful of plays. You get to have a peaceful and well-run country one of two ways. Either said "nation" is composed of a largely similar genetic stock (i.e. everyone's of the same "ethnic" group by and large) or you have a panoply of humanity who, despite that, all kneel before and worship the same God. If both of these aren't the case? Well, the blood will flow freely, frequently, and logically unnecessarily until one of them is in the long run. I don't like this, but history time and again states this to be the case.
So I'd beseech any who get that to get on the real "right side of history" as the haters of the truth/Christ so often state they are. Confess that Jesus is the Christ and God has risen him from the dead. Truly, honestly, earnestly. Renounce Satanic "privilege" and embrace the heavy yet ultimately negligent weight of penance for thy sins. You'll find yourself far happier overall if ya do
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