The story about how Christianity effected a transvaluation of values is wonderfully told in Tom Holland's much discussed book Dominion: How the Christian Revolution Remade the World.
Holland grew up loving pagan antiquity, the history of the ancient Greeks and Romans. The same affection Nietzsche had. This love drew Holland into his historical research as an adult, his expertise in the Greek and Roman eras. And yet, it was those studies that eventually, and unexpectedly, culminated in Holland writing a massive history of Christianity's impact upon the world, the West in particular, down to this very day.
Holland grew up loving pagan antiquity, the history of the ancient Greeks and Romans. The same affection Nietzsche had. This love drew Holland into his historical research as an adult, his expertise in the Greek and Roman eras. And yet, it was those studies that eventually, and unexpectedly, culminated in Holland writing a massive history of Christianity's impact upon the world, the West in particular, down to this very day.
This insight occurred to Holland, who is not a confessing Christian, when he began to compare his historical heroes, the Greeks and Romans, with his own modern, liberal, and humanistic sensibilities. The two worldviews clashed, and Holland began to wonder where the conflict originated. Here's Holland summarizing this dawning awareness in an article that anticipated the publication of Dominion:
The years I spent writing these studies of the classical world – living intimately in the company of Leonidas and of Julius Caesar, of the hoplites who had died at Thermopylae and of the legionaries who had triumphed at Alesia – only confirmed me in my fascination: for Sparta and Rome, even when subjected to the minutest historical inquiry, did not cease to seem possessed of the qualities of an apex predator. They continued to stalk my imaginings as they had always done – like a tyrannosaur.The Christian revolution was a transvaluation of the values of pagan antiquity. Our values in the West are not the values of ancient Sparta or Rome. Our values in the West are unmistakable Christian. We value equality over hierarchy. We value care over oppression. We value kindness over exploitation. We value love over might. Notions of "good" and "bad" in classical antiquity have been flipped upside down.
Yet giant carnivores, however wondrous, are by their nature terrifying. The longer I spent immersed in the study of classical antiquity, the more alien and unsettling I came to find it. The values of Leonidas, whose people had practised a peculiarly murderous form of eugenics, and trained their young to kill uppity Untermenschen by night, were nothing that I recognised as my own; nor were those of Caesar, who was reported to have killed a million Gauls and enslaved a million more. It was not just the extremes of callousness that I came to find shocking, but the lack of a sense that the poor or the weak might have any intrinsic value. As such, the founding conviction of the Enlightenment – that it owed nothing to the faith into which most of its greatest figures had been born – increasingly came to seem to me unsustainable...
“We preach Christ crucified,” St Paul declared, “unto the Jews a stumbling block, and unto the Greeks foolishness.” He was right. Nothing could have run more counter to the most profoundly held assumptions of Paul’s contemporaries – Jews, or Greeks, or Romans. The notion that a god might have suffered torture and death on a cross was so shocking as to appear repulsive. Familiarity with the biblical narrative of the Crucifixion has dulled our sense of just how completely novel a deity Christ was. In the ancient world, it was the role of gods who laid claim to ruling the universe to uphold its order by inflicting punishment – not to suffer it themselves.
Today, even as belief in God fades across the West, the countries that were once collectively known as Christendom continue to bear the stamp of the two-millennia-old revolution that Christianity represents. It is the principal reason why, by and large, most of us who live in post-Christian societies still take for granted that it is nobler to suffer than to inflict suffering. It is why we generally assume that every human life is of equal value. In my morals and ethics, I have learned to accept that I am not Greek or Roman at all, but thoroughly and proudly Christian.
This transvaluation of values makes the earliest writings in the Christian canon, the letters written by St. Paul, among the most revolutionary documents in the history of world.