Christianity can exercise its influence on the souls of men, it can help fortify an understanding of liberty as a "liberty under God," [as opposed to liberty of the will] only if it rejects the temptation to become a wholly "democratic" religion.
This is so because a wholly democratic religion would turn Christianity into nothing more than another mirror of the popular will. In a wholly democratic religion the popular will makes up its own God on its own terms (or, as under Communism or Ayn Rand Libertarianism, the church is thrown out and man/state declares itself God). This is happening within the church in the West today, as Edward Norman discusses in Secularisation:
Thus a secularised version of the love of neighbor is released from the constraints of an articulated moral system--least of all from one claimed to be of divine origin--and elevates human need as a sovereign principle. Once Christ is represented as primarily concerned with justice and welfare, rather than with sin and corruption, the equation of his religion with the leading tenets of modern Humanism is easily effected. Humanism, however, in whatever guise it presents itself, is about the sovereignty of humanity and its imagined needs, and not about the demands of God at all. It is not only inherently an enemy of authentic Christianity, but also its probably successor.
...Once humanity and its needs have been elevated to sovereign determination of public and private action, anything that can be represented as an affront or an impediment to the painless existence of men and women is made to seem morally unacceptable--an outrage. Morality then appears as self-evident: it is the palliation of whatever humans themselves regard as the cause of their suffering or deprivation.
It is worthwhile to note that when morality appears self-evident, we probably already have a problem.
The same risk--that the church and the state/popular will become one--holds true under despotic governments as it does under democracies. Whether it be the Holy Roman Empire, 1930's Germany, France after the Revolution, any Communist state, any Islamic state, Czarist Russia, Henry VIII, or an Ayn Rand Libertarian state--in every case religion and the state are one and the same, and if it's a Christian state it is a church that has been usurped by the state.
Among history's philosophies and religions that guide governance only Christianity provides the freedom of conscience necessary for the separation of church and state. Either Christians follow Christ which has nothing to do with the state (Mark 12:13-17), or "the church" and the state become one in the same just as it would under Communism or in an Ayn Rand Libertarian state. The church is often usurped by the state for political purposes as it was under the Holy Roman Empire, the Spanish Inquisition, Henry VIII, Czarist Russia, etc. but in every instance is a rejection of Mark 12:13-17.