Christian life in the centuries prior to the Constantinian conversion was already developing authoritative structures, and at a relentless pace. Such structures are always necessary for governance, spiritual and temporal. The general tendency of these structures was expansion, away from the margins and into the center of human affairs.
More.
Certain partisans will object strenuously to the idea that pagan Rome lent the universalist impulse to Christianity, but they will be wrong.
They are already unwilling to accept that the aims of the historical Jesus were more modest, who insisted he was sent only to the lost sheep of the house of Israel (Matthew 10), whose twelve disciples were to judge the twelve tribes of Israel in the imminently coming eschatological kingdom of God (Matthew 19) in Jerusalem. To it many in Israel were called, but only few were chosen.
The germ of the universal religion idea certainly came from elsewhere, from the likes of St. Paul the Roman citizen and his intellectual and spiritual kin who, inspired by Isaiah the prophet among others, thought God's aim was to have mercy on all the nations (Romans 11).
For his part, Paul combined in himself two streams with a single and much more ambitious agenda. The Hellenistic Jew of the proselytizing Pharisee variety not coincidentally was still the enthusiastic missionary despite a crisis of conversion, but with a now much wider field of opportunity. And the Roman citizen by birth who was at liberty to travel and study in Jerusalem became himself an itinerant teacher, exploiting his favored position both at the margins and finally at the center of the empire.
My ambition has always been to preach the Good News where the name of Christ has never been heard, rather than where a church has already been started by someone else. ... In fact, my visit to you has been delayed so long because I have been preaching in these places. But now I have finished my work in these regions, and after all these long years of waiting, I am eager to visit you. I am planning to go to Spain, and when I do, I will stop off in Rome. And after I have enjoyed your fellowship for a little while, you can provide for my journey. But before I come, I must go to Jerusalem to take a gift to the believers there.
-- Romans 15:20ff.
Ahmari chalks it all up to the divine will. The evidence chalks it up to the civis romanus and Pharisee.
