During the French Revolution, radicals made no bones about attacking the Church as a source of oppression and an obstacle to progress. Marxists, of course, were hostile to religion of all types, but they really hated Christians. In America, direct attacks on Christianity started in the early 20th century, as progressives abandoned the Social Gospel, in order to bring Jews into their movement. The point being, the Left has always had it in for Christianity.
We no longer have Jacobins. We still have a few Marxists kicking around, but they are mostly museum pieces. Exactly no one in a position of authority in the West embraces Marxism or communism. As for progressives, we have plenty of them in America, but their thing has morphed into a weird identity cult that hates white people. Of course, there are precious few Christians around, at least in the ruling classes. In fact, it is hard to find any Christian leaders in the West.
The West is post-Christian now. Leaders of all Western countries agree that Christianity has nothing to offer, in terms of public affairs. You never hear any of them make appeals to the deity or make references to Christian teaching. Every Western nation embraces some form of liberal democracy. Some nations lean toward social democracy, while others embrace neo-liberalism. American leaders will occasionally mumble something about freedom of religion, but otherwise, we are ruled by non-Christians.
The thing is, Christianity brought together certain cultural and political elements that made liberalism possible. There is a reason that things like equality before the law and representative government never took root in Africa. The Roman Republic and ancient Athens had some features of liberal democracy, but they were largely ruled by a collection of families of equal rank. While the Greeks were produced great genius, they did not produce liberal democracy.
To understand this, we need to start with God. The ancients were sure the gods picked sides, played games with man and did so without a grand plan. That means the gods did not see all men as being equal. Jews, of course, were really sure God picked sides, their side, as they are the chosen people. It was the Christians that refined the idea that all men were in equal in the eyes of God. That is the foundation of equality before the law and egalitarianism, at least as far as natural rights.
Another idea, essential to liberal democracy, is the concept of an ordered universe with fixed rules. This was a concept borrowed from Greek philosophy and carried through Europe by Christianity. Not only is an orderly universe essential for the development of science, but it is also essential for the development of rational government. If God has created an orderly universe, governed by immutable and discoverable laws, human society should follow those rules.
You cannot have a free society without contracts. The bargain between men certainly predates Christianity, but it was the Jews who produced the idea of a covenant, a contract that even God would abide. Christians inherited this. The idea that making a contract and sticking to it, because it would displease God to do otherwise, makes it possible to enforce contracts. You cannot have anything resembling liberalism without contract law.
Finally, morality without the divine is just a set of man made rules. Christians were certainly not the first to ascribe the moral code to the supernatural, but they expanded on the Jewish concepts to create a whole body of morality that elevated humanity in the eyes of God. Doing the right thing by your fellow man, even when no one is looking, because God will judge you in the afterlife, allows for the development of the hidden law, a moral code. It allows orderliness to spring forth organically.
That is an extremely broad overview, but the point is that what we take for granted about liberal democracy, has its roots in the Christian past. Within one lifetime ago, Western people expected to be ruled by Christian men. Even when the rulers were not very Christian, they kept it to themselves. It was just accepted that public character tracked with Christian morality. Now that we are ruled by post-Christian women, how long before all of these ideas wither away?
We certainly see some unraveling with the modern notion of egalitarianism. We have gone from men being equal before God, to all people being equal to each other. Lacking the limiting principles that come with religion, progressives are a click away from demanding that all of us pretend we are exactly the same. The story Harrison Bergeron has gone from satire to divine scripture. The Christian regard for the complexity of God’s creation has been completely lost in the post-Christian age.
We are seeing the return of occasionalist magic in the modern era. When the Left talks about “institutional racism” or “white privilege”, they are not talking about definable things that one can measure. These are mystery forces acting on man in the same way Old Scratch used to play the role of trickster. The difference is they assume humans lack the agency to resist these mystery forces. In many respects, Norse pagans were more empirical than the modern progressive.
This is a big topic, but it is something that is worth examination. It is assumed that the stock of human knowledge is always growing, but that does not mean nothing is lost. Western people have abandoned a large chunk of knowledge that had been formalized in Christianity. Some of it can be replaced with science, but the parts underpinning civil morality and our moral philosophy are not easily replaced by secular alternatives. Like the game Jenga, we may have removed a vital peg from liberalism.