I don't quite understand what Ganymede is trying to prove. Christianity is an independent religion and did not originate from any paganism. To say so is simply foolish.
Well, maybe it is foolish, of course. I just look at the subject from a slightly different perspective. For you, as a believer, it's foolish in any case, even if it's true. But for me, as a "non-believer," it's a fact that I see clearly. Who is right? And is this truth even necessary? There is faith and disbelief, everything else is just "adjectives":)
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"So much has gone
and little is new"
David Bowie