In any previous empire the religion of the ruling class had always been distinct from the faith of the subjugated masses, so the Christian emperors’ attempt to impose their theology on their subjects was a shocking break with precedent and was experienced as an outrage.

Christianity may well have succeeded even if Constantine had not converted.

How could the Christian Church, apparently quite willingly, accommodate this weird megalomaniac [Constantine] in it's theocratic system? Was there a conscious bargain? Which side benefited most form this unseemly marriage between church and state? Or, to put it another way, did the empire surrender to Christianity, or did Christianity prostitute itself to the empire? It is characteristic of the complexities of early Christian history that we cannot give a definite answer to this question.

Christianity had undermined all the temples of idolatry, and was enthroned as the established religion of the Roman empire. Ambitious men rallied about it as a great political power. Wicked men nominally embraced it as an essential step to worldly advancement. Christianity had thus, perhaps, more to fear from favoritism than from persecution. Unprincipled men, grasping at wealth and power, embraced Christianity merely as an instrument for the promotion of their own temporal aggrandizement. They hated its spiritual teachings, and endeavored to make it a religion of dead doctrines and of pompous ceremonies, rather than a rule to govern heart and life. They crucified Christianity while crowning it.

If it be asked why Judaism, then, was not made the religion of the empire, instead of Christianity, which it hated with all the fervor of close relationship, the answer is at hand: Judaism laid no emphasis on its cosmopolitan features, and discouraged belief in the historical fulfilment of its own prophecy.

If only the self-deluded but fervent-spirited Muhammad, whose soul was stirred within him when he saw his fellow town-men wholly given to idolatry, had been brought into association with the purer form of Christianity ... he might have died a martyr for the truth, Asia might have numbered her millions of Christians, and the name of Saint Muhammad might have been in the calendar of our Book of Common Prayer ... Think, then, of the difference in the present condition of the Asiatic world, if the fire of Muhammad's eloquence had been kindled, and the force of his personal influence exerted on the side of veritable Christianity.

Christianity, with its strong emphasis on unity under one God (an emphasis that it shares with Islam), can seem an almost natural ally of empire—unless, of course, the prophetic-critical dimension of the biblical tradition, which the Jesus of the synoptics certainly represented, is allowed a hearing. But as the history of Christology in the West easily demonstrates, after the establishment of Christianity, the prophetic office of the Christ, based not only on Jesus’ teaching but (even more so) on his suffering at the hands of power, was definitely subdued in favor of his priestly and kingly offices. Triumphant peoples, successful peoples, possessing peoples—empires!—do not want crucified criminals as their chief cultic symbol, especially not when they themselves are the crucifiers ... as they regularly are!

There was something called Christianity.

If only the Church had the sense to allow so many different and seemingly contradictory approaches to God, how much saner its history would have been!

... it might have resulted far better for mankind if Greece had been the source of the religion of modern civilization, and not Palestine

"In The Bloudy Tenent, Williams points out that Constantine "did more to hurt Christ Jesus than the raging fury of the most bloody Neroes." at least under the Christian persecutor Nero, who was rumored to have had the Apostle Paul beheaded and Saint Peter crucified upside down, Christianity was a pure (if hazardous) way of life. But when Constantine himself converted to Christianity, that's when the Church was corrupted and perverted by the state. Williams explains that under Constantine, "the gardens of Christ's churches turned into the wildernesss of national religion, and the world (under Constantine's dominion) to the most unchristian Christendom." Legalizing, legitimizing the Church turned Christianity into just another branch of government enforced by "the sword of civil power," i.e., through state-sponsored violence."

The Christian takes Christianity for something it never was: the teachings of Jesus.

John Howard Yoder makes the striking observation that after the Constantinian shift the meaning of the word "Christian" changes. Prior to Constantine it took exceptional courage to be a Christian. After Constantine it takes exceptional courage not to be counted as a Christian. ... After the Constantinian establishment, Christians knew that God was governing the world in Constantine, but they had to take it on faith that within the nominally Christian mass there was a community of true believers. No longer could being a Christian be identified with church membership, since many "Christians" in the church had not chosen to follow Christ. Now to be a Christian is transmuted to "inwardness."

Constantine declared his own will equivalent to a canon of the Church. According to Justinian, the Roman people had formally transferred to the emperors the entire plenitude of its authority, and, therefore, the emperor’s pleasure, expressed by edict or by letter, had force of law. Even in the fervent age of its conversion the empire employed its refined civilization, the accumulated wisdom of ancient sages, the reasonableness and subtlety of Roman law, and the entire inheritance of the Jewish, the pagan, and the Christian world, to make the Church serve as a gilded crutch of absolutism. Neither an enlightened philosophy, nor all the political wisdom of Rome, nor even the faith and virtue of the Christians availed against the incorrigible tradition of antiquity. Something was wanted, beyond all the gifts of reflection and experience — a faculty of self government and self control, developed like its language in the fibre of a nation, and growing with its growth. This vital element, which many centuries of warfare, of anarchy, of oppression, had extinguished in the countries that were still draped in the pomp of ancient civilization, was deposited on the soil of Christendom by the fertilising stream of migration that overthrew the empire of the West.