I'm sorry this is not getting more headlines.
The Edict of Milan was a huge turning point in the history of the world.
It was the first edict of religious toleration.
For the first time in history, citizens did not have to participate in the state religion.
Christianity made this idea possible.
Whereas in other religions, there is a stated political regime associated with it, there is none in Christianity.
Christianity is flexible in its arrangement with the political.
You can have a regime where religion and the state are strongly united (not one that I recommend!)
Or you can have a regime where religion and the state have a mutual hands off.
And by that, I don't mean that individuals can't participate in secular life based on their personal values.
But the Church doesn't tell people how to vote, or support a given ideology, and the state doesn't try to run the Church.
That's my preferred model.
If Christianity had had a political agenda, I don't think the Edict of Milan would have been possible, nor do I think it would have spread so easily. Its flexibility by political elites made it an easier sell throughout the ages.