Arianism and the "Son of God" thing. Willibrord and Bonifatius did not find pagan German tribes but christian Arianic converts
Early in the 4th century the question whether Christ really was the son of God was not settled in circles of christian converts. The Alexandrian presbyter Arius has become the most famous of those who held that Christ is not truly divine but a created being. Arius' basic premise was the uniqueness of God, who is alone self-existent and immutable; the Son, who is not self-existent, cannot be God. Because the Godhead is unique, it cannot be shared or communicated, so the Son cannot be God. Because the Godhead is immutable, the Son, who is mutable, being represented in the Gospels as subject to growth and change, cannot be God. The Son must, therefore, be deemed a creature who has been called into existence out of nothing and has had a beginning. Moreover, the Son can have no direct knowledge of the Father since the Son is finite and of a different order of existence.
Exactly this denial of sonhood makes "Arians", as they became to be called after disciplinary measures for "christian" doctrinal unity were taken at Nicaea (AD 325), true believers in the view taken later by the prophet Muhammed. Muhammed's charisma was such that he did not need special status by claiming to be son of God or doing miracles. "Watch flying birds", he said, "they are miracles enough" Koran 67:13.
Despite post-Nicaean trinitarian propaganda, it took long before the trinity claim was forced upon all christians. In the meantime, Arianism spread towards the Northern European German tribes, were it fitted much better in the basically down-to-earth empirical religious metaphysics of Germanic culture. Missionaries like Willibrord and Bonifacius, on the record for having converted the Germanic tribes to christianity did, in truth, not find pagans, but christian Arians.
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