It is a fallacy that religion is your private affair and it had nothing to do with the state affairs. And this secular vision brought chaos in every corner of the world . Rather Islam is a complete code of life . whether it is social or state affairs ,material or spiritual ,Islam guides man in every walk of life .
There are various ways of governance like monarchy, oligarchy, democracy and dictatorships. The best was the one which State of Madinah had. Islamic State follows rule set up by Almighty and Prophet Mohammad PBUH. The duties and functions of a Muslim state seem to be following
Legislation .God is the supreme legislator. After that Prophet Mohammad PBUH taught theological dogmas to his adherents. He also gave them laws concerning all activities of life , individual as well as collective , temporal as well as spiritual. Quran is the words of Allah and therefore it should be a constitution for Muslim states. Even the Muslim law of war is humane . It does not permit the killing of women ,child ,very old ,sick and even trees. The laws of God are everlasting because inferior authority cannot change the law and no one is superior than God.
In the domain of judiciary, all men are equal before law. Non-Muslims inhabitants of Islamic State enjoy a judicial autonomy.The head of the Muslim state should not be above the law and history shows every Muslims leader have to appear before the courts for accountability. The Quran says that the Jews should apply the Biblical laws and the Christians those of the Gospel .
In Executive, the sovereignty belongs to God ، and it is the trust which is administered by man, for the well being of all without exception.
As far as the Economic system is concerned,Islam desires the circulation of wealth among as large a number of people as possible. Islam wants a society free of interest . Islam favoured system of Zakat which is a tax for the needy and destitute. It impose heavier obligations on rich and they have to pay heavy tax . Islam admonished to beg charity , and it would be a source of shame on the day of resurrection. God permit the trading and forbidden interest.
In Muslim State , non-Muslims are treated well. The first and foremost is their right of vote in election of the head of the State . Non-Muslims have been holding the rank of minister in Muslim state. During the caliphate they were given high official ranks . In the time of the Abbasid caliphs ,we find the Christian patriarch and the Jewish hakham , among the highest dignitaries of the state ,connected directly with the caliph .Omer-bin-Khattab put a Christian at the head of his administration in Madinah. He also wrote to the governor of Syria : Send us a Greek who could put in order the accounts of our revenues. More than this , The same caliph often consulted non-Muslims on military , economical and administration questions. In the time of second caliph , certain Muslims had usurped a piece of land belonging to a Jew , and had constructed a mosque on the site. Learning this news , the caliph ordered the demolition of the mosque and restoration of the land to the Jew. In Islamic State, non-Muslims were given liberty of practicing customs entirely opposed to those of Islam. In a nut shell, Islamic State suggests black has no superiority over white Vice versa and Arab has no superiority over non-Arab and vice versa . Piety would be criterion on the day of Judgement.
In an Islamic State , the leader is the one who is easily approachable to every man in the street. Even an unlettered man can meet him at a particular place , most probably a Mosque where their issues are solved. He remains in touch with the public opinion. A leader is a one who never leaves his state without a Amir. Like when Mohammad PBUH used to leave his state for any purpose , he always appointed a Amir who had the control over the State . A leader protects right of wealth , health, Education and honor of his citizens. A leader is the one who says I ll be responsible for the deceased dog died near Euphrates River. A leader is the one who used to wander to have a look at his public at late nights.. A leader should take decisions based on opinion of the people of learning , knowledge and experience but last say should only belong to the Leader.