Christianity while implementing a theocracy of sorts throughout its history has distanced itelf from such an approach in modern times preferring seperation of state and religion
I would say its more firmly rooted in the tradition than that. The New Testament, and the Christian Revelation in general, has no laws to put forward for the purpose of determining temporal legislation.
As any Protestant will tell you, Pauline theology spurns the "works of the law", which are dead, in favour of grace.
Throughout the medieval period, the secular law codes were based variously on Saxon, Roman and other legal norms because the religion itself lacked a divinely revealed legal system. Canon law can be changed by any pope. It's mutable, not an immutable divine code.
Sure, laws could be adapted to be more in keeping with Christian ethics but there wasn't an actual Christian "law" akin to Sharia that anyone could point to and say, "yeah, God wants us to divide inheritance up as follows" or dish out "xyz" punishment for such-and-such a crime.
In 866, the pagan Khan Boris of the Bulgars wanted to convert to Christianity and sent a letter to Pope Nicholas asking him to explain the "law of the Christians" so that he could live by it.
The pope replied as follows:
The Responses of Pope Nicholas I to the Questions of the Bulgars A.D. 866
Now then, at the very beginning of your questions, you properly and laudably state that your king seeks the Christian law...One should know that the law of the Christians consists in faith and good works. For faith is the first of all virtues in the lives of believers. Whence, even on the first day there is said to be light, since God is portrayed as having said: Let there be light,[Gen.1:3] that is, "let the illumination of belief appear." Indeed, it is also because of this illumination that Christ came down to earth. Good work is no less demanded from a Christian; for just as it is written in our law: Without faith it is impossible to please God,[Heb. 11:6] so it is also written: Just as a body without a spirit is dead, so, too, faith without works is dead.[James 2:20] This is the Christian law, and whoever keeps this law properly, shall be saved.
He proceeds to explain in subsequent that Christians have no laws covering dress, diet or in terms of legal punishments. Indeed he invites the Khan to have a read of Justinian's Institutes of Roman Law as a model. A particularly amusing interchange came in answer to question LVIIII by the Khan:
We consider what you asked about pants (femoralia) to be irrelevant; for we do not wish the exterior style of your clothing to be changed, but rather the behavior of the inner man within you, nor do we desire to know what you are wearing except Christ — for however many of you have been baptized in Christ, have put on Christ [Gal. 3:27] — but rather how you are progressing in faith and good works
Likewise, when Jesus was asked by someone to act as arbiter in a family property dispute, he completely disowned even a modicum of interest in telling people how to run their own lives in that way:
Someone in the crowd said to him, “Teacher, tell my brother to divide the inheritance with me.” 14But he said to him, “Man, who made me a judge or arbitrator over you?”
And he said to them, “Take care! Be on your guard against all kinds of greed; for one’s life does not consist in the abundance of possessions.” 16 Then he told them a parable... (
Luke 12:13-14)
In other words, whereas
Numbers 27:7-11 (which says a man's sons inherit first, daughters if no sons, brothers if he has no children, and so on) in the Torah and Sura 4 of the Qur'an have extensive details about inheritance law, Jesus prioritizes ethical living over the legal details and sees the development of law as a human responsibility, not a religious one. That's just a difference in mindset about the role of divine law but its an important one for Christians.
Eastern Christianity was, for a time, a bit more theocratic, inasmuch as you had caeseropapism - a sacral emperor and a sort of kingdom of God on earth, like the Sunni caliphate.
Western Christianity, both Catholic and Protestant, was fundamentally different.
The Western half of the Roman Empire collapsed and religious authority in the abandoned West became consolidated in the papacy.
When the Holy Roman Empire of the Germans under the House of Hohenstaufen tried to impose a similar caeseropapist system in Europe in the 11th century, and were investing bishops (i.e. performing religious functions), the papacy under Gregory VII resisted and this sparked the century long investiture conflict between church and state.
The resulting Concordat of Worms in 1112 circumscribed the powers of both, preventing the Emperor from issuing canonical laws in the ecclesiastical courts or investing bishops and the Papacy from interfering with the secular courts or having any direct role in public affairs, out with the limited domain of the Papal States.
As a result, secular law - already compiled from Justinian's Roman codex and customary law such as English Common Law - diverged even further under royal control from the canons of the church. Because the pope denied the Emperor any sacral authority, he had to justify his law codes based upon secular rationales as did every other King in Christendom.
Thus in the Islamic world, the study of law (jurisprudence) was bracketed under theology, because it was a matter of shariah. In medieval universities, they were studied as distinct academic disciplines.