The last great formal persecution of Christians in the Roman Empire ended in AD 303.
Ten years later, Christianity was legalized by Constantine I. After this structural change, Christianity increasingly accepted, and even defended, the dominant social order, especially concerning war and money. Morality became individualized and largely sexual.
The Church slowly lost its free and alternative vantage point. Texts written in the hundred years preceding 313 show it was unthinkable that a Christian would fight in the army, as the army was killing Christians. By the year 400, the entire army had become Christian, and they were now killing the pagans.
Before AD 313, the Church was on the bottom of society, which is the privileged vantage point for understanding the liberating power of the Gospel for both the individual and for society. Overnight the Church moved from the bottom to the top, literally from the catacombs to the basilicas. The Roman basilicas were large buildings for court and other public assembly, and they became Christian worship spaces.
The Christian church became the established religion of the empire and started reading the Gospel from the position of maintaining power and social order instead of experiencing the profound power of powerlessness that Jesus revealed.
In a sense, Christianity almost became a different religion! This shift would be similar to reversing the first of the 12 Steps to seek power instead of admitting powerlessness. In this paradigm only the 'winners' win, whereas the true Gospel has everyone winning. Calling this power 'spiritual' and framing success as moral perfection made this position all the more seductive to the ego and all the more disguised.
The failing Roman Empire needed an emperor, and Jesus was used to fill the power gap, making much of his teaching literally incomprehensible and unhearable, even by good people. The relationships of the Trinity were largely lost as the very shape of God: the Father became angry and distant, Jesus became the needed organizing principle, and for all practical and dynamic purposes the Holy Spirit was forgotten. An imperial system needs law and order and clear belonging systems more than it wants mercy or meekness or transformation.
By the grace of God, saints and holy ones of every century and in every denomination and monastery still got the point, but only if they were willing to go through painful descent--which Catholics call 'the way of the cross,' Jesus called 'the sign of Jonah,' Augustine called 'the paschal mystery,' and the Apostles' Creed called 'the descent into hell.' Without these journeys there's something essential you simply don't understand about the very nature of God and the nature of your own soul.
You try to read reality from the side of power instead of powerlessness, despite the fact that God has told us (through the image of the Crucified) that vulnerability and powerlessness is the way to true spiritual power. But Christians made a jeweled logo and decoration out of the cross, when it was supposed to be a shocking strategic plan, charting the inevitable path of full transformation into God.
