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Please explain why this is heresy. And if you say it derives from Greek mythology, please document which myths

Nicenism is a failing effort to reconcile Jewish Unitarianism with ancient Greek Mythology and Philosophy. Justin Martyr introduced eternal generation into the Christian concept. See for example his debate with Typro the Jew.

Look the said debate up, if you want to..

But Justin Martyer is responsible for this error, do you know who that is ?