The conception of just war and its relationship to the state is indispensable in both Christian and Islamic political thought. Since both Christians and Muslims set up right authority as a condition for just war, and further, they take this authority from the hands of the individual and locate it in the ruling power of the community, it is important to understand what the aims and purpose of the community are conceived to be if we are to understand the end towards which war might be applied. It is precisely in the purpose of the state that Christianity and Islam take drastically different directions. While there are many differences that are worth examining, the most important difference lies in the relationship between the temporal and spiritual powers or authorities. At first glance, it seems possible that Christian and Islamic theories may have a lot of commonalities; both recognize a distinction between the secular and religious realms. However, the difference between the two systems of thought lies in the relationship between these realms as well as in their final ends.
Augustine famously distinguished between the city of God and the city of man. This distinction carried over into the medieval period, although the meaning of the two cities and their ends often fluctuated according to the current political and religious climate. At times this distinction was taken to be that between church and state, and at times between saved and unsaved men. It is important to understand exactly what Augustine meant by his distinction and whether or not this distinction can still be made.
Augustine distinguishes between the two cities by examining the objects of their love. The cities are made up of a body of men that share a common object of love. He says,
Two cities, then, have been created by two loves: that is, the earthly by love of self extending even to contempt of God, and the heavenly by love of God extending to contempt of self. The one, therefore, glories in itself, the other in the Lord; the one seeks glory from men, the other finds its highest glory in God."
It is important to dispense with the notion that the city of God can be identified with the visible church. Augustine defines the city as “a fellowship of godly men…in [it], love of God has been given pride of place.” He includes in this definition all the good angels, as well as the souls of all those who have died having in faith in God. He also makes it clear that there are some members of the visible church who are in fact not members of the city of God. He states that, “while she is a pilgrim in this world, the City of God has with her…some who will not be with her to share eternally in the bliss of the saints.” From the Fall of man until the Final Judgment, the city of God and the city of man will be mingled together on earth and it will not be until the end that God will separate the cities and give them their eternal rewards and punishments.
Augustine defines the city of man as a fellowship of the ungodly, who has given pride of place to self-love. It is equally important to note that the city of man is not identical to Rome, Babylon, or any political power, nor is it the sum of all the powers of the earth combined. Rather, the city of man is composed of all the unsaved—be they angels or men, living or dead. The city of man is concerned with temporal pursuits and powers and pleasures of the present age, neglecting the future and eternal destiny that awaits it. Next up...the citizens of Augustine's cities.