Jesus (PBUH) was not entrusted authority with administrative tasks. Therefore, in Christianity, there were no decrees with regard to the state administration. There were only principles pertaining to faith and morality.
Yet showing them as if they really existed, clergymen invented decrees in Bible that would enable them to rise in power to take hold of the ruling body. To this end, by picking out social rules and political principles of common usages and of old holy books of previous times, they added these to the Bible. In other words, they made changes in the religion that Jesus (PBUH) conveyed. From then on, clergyman started to govern the Christian peoples. Therefore, the state of clergy appeared. This kind of ruling was called theocracy.
A theocratic body introduced the notion of unconditional submission and a blind obedience to the clergyman. Later on, it transformed into a kind of rule in which clergymen and spiritual leaders put pressures.
As is obvious, theocracy is the rule of the clergymen of the Middle Ages. In Islam, there is no such a way of government. In the way of state and administration that it introduces, it is not possible to see the traces of despotism, oppression, and pressure. The administrative way that Islam accepts and applies to is republican (tending to the public). A governing party and formation come to power through election. The Era of Bliss is clear evidence to this. The understanding of republicanism of the Era of Bliss was not composed of only a title and of a vision. It was a real Religious Republic.
The Prophet Muhammad (PBUH) not only conveyed the Hereafter-oriented principles such as faith and morality as Jesus (PBUH) did, but also conveyed the verdicts of faith, morality, and politics that organize worldly life and the life beyond the grave altogether. He informed about even most delicate points and showed them personally through practice. In Islam, the religion has never been a means of pressure as in other religions, on the contrary, has become a means of any sort of material and spiritual bliss.
Throughout the history of Islam, no mullahs or religious scholars claimed authority in the state administration. They have just delivered their opinions about the actions of the governors whether if they were appropriate to Islam or not.
Furthermore, in Islam, there are no such things as unconditionally submitting to the every word of the rulers and blindly obeying them. Muslims were able to call the Caliph into account and want him to explain certain points. The Caliph Omar had a number of practices in this respect. Muslims were able to warn this person, who is at the top government, by saying If you swerve from the true path, we shall put you right with our swords. The Caliph Omar became pleased with this kind of warnings and stated his gratitude to them.
All these points show that theocracy has nothing to do with Islam at all.