Much of what Jesus taught seems to have been followed closely during the first several hundred years after his death and resurrection. As long as Jesus’ followers were on the bottom and the edge of empire, as long as they shared the rejected and betrayed status of Jesus, they could grasp his teaching more readily. Values like nonparticipation in war, simple living, inclusivity, and love of enemies could be more easily understood when Christians were gathering secretly in the catacombs, when their faith was untouched by empire, rationalization, and compromise.
.. The last great formal persecution of Christians in the Roman Empire ended in 311 CE. In 313, Constantine (c. 272-337) legalized Christianity. It became the official religion of the Roman Empire in 380. After this structural change, Christianity increasingly accepted, and even defended, the dominant social order, especially concerning money and war. Morality became individualized and largely focused on sexuality. 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 313, the church was on the bottom of society, which is the privileged vantage point for understanding the liberating power of Gospel for both the individual and for society. Within the space of a few decades, 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.
.. When the Christian church became the established religion of the empire, it 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!
The failing Roman Empire needed an emperor, and Jesus was used to fill the power gap. In effect, we Christians took Jesus out of the Trinity and made him into God on a throne. An imperial system needs law and order and clear belonging systems more than it wants mercy, meekness, or transformation. Much of Jesus’ teaching about simple living, nonviolence, inclusivity, and love of enemies became incomprehensible. Relationship—the shape of God as Trinity—was no longer as important. Christianity’s view of God changed: the Father became angry and distant, Jesus was reduced to an organizing principle, and for all practical and dynamic purposes, the Holy Spirit was forgotten.
Spirituality is primarily about human transformation in this life, not just salvation in a future realm. While Western Christianity lost much of this emphasis, and became rather practical and often superficial, the Eastern church taught theosis or divinization as the very real process of growing in union and likeness with God in this world.  This is one of the many losses Christianity experienced in the Great Schism of 1054, when the popes of East and West mutually excommunicated one another.
.. Pope John Paul II was acknowledging that the Western church had largely lost its foundational belief in divinization, and in the practical order had even denied its possibility. Instead, we were just “sinners in the hands of an angry God” and even “totally depraved.” No wonder humans suffer from such lack of self-esteem today. We haven’t told them the central and foundational Good News! I believe this is the source of a lot of the anger and disillusionment with Christianity today.