Is the Son truly God?
The Arian controversy begins
A priest named Arius is teaching in Alexandria, and what he teaches is elegant and logical and — according to his bishop — wrong.
The question Arius is trying to answer is one of the hardest in Christian theology: how can there be one God and yet the Father and the Son both be divine? His solution is to conclude that the Son is not fully God — he is the highest of all created beings, the firstborn of all creation, the one through whom God made everything, but there was a time when the Son did not exist. Before the Father created him, he was not.
The slogan Arius's followers use is catchy and memorable: there was when he was not.
Bishop Alexander of Alexandria calls Arius in and tells him this is wrong. Arius disagrees and keeps teaching. Alexander holds a synod. The synod condemns Arius. Arius appeals to other bishops, and the dispute, which started in a single church in Alexandria, spreads with astonishing speed across the entire eastern empire.
Why does it spread so fast? Partly because Arius is brilliant and persuasive. Partly because the question is genuinely difficult. And partly because Arius writes his theology into popular songs — catchy, memorable hymns for sailors and travelers and merchants to hum while they work.
Soon the songs are everywhere. The theological dispute has gone viral.
Constantine, freshly victorious and wanting a unified empire, is horrified. He writes to both sides urging them to stop. Neither side can stop. The stakes are too high.
He calls a council.
“There was a time when the Son was not.”
— Arius of Alexandria, c. 318 AD
“In the beginning was the Word, and the Word was with God, and the Word was God.”
Arius's teaching was not obviously wrong to everyone who heard it. It solved a real logical problem — the problem of how one God can have a divine Son — by making the Son less than fully divine.
The church spent the next sixty years working out why this mattered, why it was not enough to have a very great creature rather than a fully divine savior. The answer, eventually, was soteriological: only God can save. If the Son is not fully God, he cannot do what salvation requires.
The question underneath the Arian controversy is the same question underneath every theological dispute the church has ever had: who is Jesus, exactly? Everything else follows from the answer.
Who do you say that he is?