Daniel Klein sets the record straight:
Olsson: But was it Christianity in particular, or monotheism more generally, that opened up the road to liberalism? Don’t other religious traditions and civilizations also have ideas on individuals, moral agency, and the conscience?
Klein: Monotheism is necessary but not sufficient. Other monotheistic religions didn’t have moral agency, moral equality, and the conscience in quite the same way. Siedentop says that Christianity was quite exceptional in the dignity it accorded the individual. That individual was a votary of the Christ with responsibility to figure out how to advance the well-being of the widest whole of humankind.
Siedentop speaks a lot about moral equality, and I think that one aspect of what he means is that everyone, no matter how depraved or religiously misguided, even an enemy, has the potential for upward vitality, and everyone, no matter how saintly and accomplished up to the present moment, has the potential for downward moral movement. Each of us faces a same sort of moral challenge all the time. Siedentop would associate this image of the individual with Augustine. The implication is that everyone is with or potentially with God, and as an individual. It isn’t about abiding by a set of ritualistic practices. It is a very individual affair.
Siedentop argues that liberalism emerged from, and best prevails today, in what was once thought of as Christendom. If you look at a map of economic freedom today, you will see that the “most free” countries generally correlate to Christendom circa 1300, plus areas (North America, Australia and New Zealand, arguably Japan) that have since been developed by or influenced by the Christian West. In a sense his book is a theory of that correlation, an explanation. Christianity made liberalism possible—which is not say that, within a country, Christianity is sufficient for, or will necessarily produce, liberalism.