In The Dark Side of the Enlightenment, John Fleming explained the argument like this:
Michelet was a determined secularist. He was, furthermore, genuinely appalled at the Christian history of his own country, which included such horrors as the Albigensian crusade and the massacre of St. Bartholomew's Day. But he was not an anti-Catholic bigot or a crude propagandist. He was trying to look deeper, to the very philosophical foundations of revolution. He finally concluded that the Revolution was founded in the concept of justice, whereas the Christian economy was founded in the concept of grace. Man had sinned. Man had been saved by the sacrifice of Jesus Christ. No merit of his own had gained his salvation; all flowed from divine grace, a gift that could never be earned. Man had no right to his salvation.
Two unfortunate implications flowed from this doctrine, and both encouraged the arbitrary at the expense of the just. The first was that human political arrangements were founded in a nexus of grace and favor. The relationships of feudalism were anything but lawless, but they sounded everywhere with echoes of the divine condescension. There was an ideological thread, however, finely spun, between the great Lord of the Heavens and the local "lord of the manor." . . .
The second baneful implication related to the clergy who, in Michelet's opinion, could hardly avoid, under such a theological system, claiming for themseles the arbitrary powers of semi-divine dispensers of sacramental grace. . . .
The Revolution, on the contrary, was legal and contractual. It claimed its basis in droit -- a word that in French bears the burden of two English words, "law" and "right." The primary document of the French Revolution is The Declaration of the Rights of Man as Citizen.
I define the Revolution: the advent of law, the resurrection of right, and the reaction of justice. . . . The Revolution is nothing but the tardy reaction of justice against the government of favor and the religion of Grace.When I read this I was immediately struck by how powerfully this symbol conveys the difference between the medieval and modern worlds. In the Middle Ages many things about the world just were. If you asked why, the only answer would be that they had always been that way. If you kept pressing, you would eventually be told that God had ordained it. Why were some people born serfs and others lords? Because this is how the world has always been. But why don't we change it? Because God made it so! The relationship between the divine order and political legitimacy was keenly understood by many Europeans across this whole period, and it was often restated in turbulent times. Perhaps the most famous formulation, and certainly the briefest, was offered by James I of England: "no bishop, no king."
And then in the modern period, rather suddenly in historical terms, these arguments ceased to persuade. Suddenly it was not enough to say that we had kings because we had always had kings, and that the order of the world must have sprung ultimately from God's hand. The injustice and unfairness of the old order suddenly rankled in a way it had not before. Suddenly there was a new standard by which the arrangements of society had to be judged: it is just? Is it fair? Is it right?
Not that everyone was persuaded by the new reasoning; indeed the history of Europe from 1789 to 1945 was a long struggle between those who accepted the reasoning of Paine and Robespierre, and those who held to the old way. This was the argument, the one that defined the politics of an age. These days the argument is effectively over on the intellectual plane, with liberals and conservatives offering different versions of the argument from justice and human rights. Michelet predicted this; now that the call to justice had been issued, he wrote, the space for Christian grace in political thinking must inevitably shrink before it. The argument from God's grace would fail in the face of the demand for justice, which, he said, is more powerful than anything. Certainly in the modern world it has been.