Augustine of Hippo (354-430) had very strong feelings about the difference between spiritual and temporal authority and structures. In his City of God he makes it clear that earthly governing structures, i.e. the State, were spiritual Babylons, equivalent to fallen and sinful institutions. The Church was the true and proper guide for mankind through this world. Had Adam and Even not sinned in Eden, mankind would have been able to live in harmony with itself and the world, and temporal structures would not be necessary. After all, the State seemed to exist in order to regulate behavior, particularly behavior that was detrimental to others. In an un-Fallen world, this would be unnecessary.
Augustine was living in a Roman Empire that was Christian-friendly, but still remembered the persecutions. His attitude on the State was likely based on his knowledge of the persecutions and of historical pagan nations, and was therefore more harsh, seeing the State as the direct opposite of the Church.
Thomas Aquinas (1225-1274, also mentioned here) took a slightly different view. He was surrounded by States with Christian rulers and was willing to consider the State without condemning it. Like Aristotle, Aquinas saw society as a natural institution for mankind, and therefore something ordained by God. The State was another form of society, and therefore was a part of man's natural inclination and therefore also was ordained by God.
Church and State were both important institutions, but not separate in their goals. For Aquinas, the Church existed to help mankind attain its spiritual goal. It did not follow, however, that the State existed to help mankind attain a temporal goal. Mankind has only one goal: a spiritual one. Therefore, the State exists to support man's spiritual goals as well. Any conflict between the actions of the two should be resolved in favor of the Church, whose primary goal is spiritual.
Dante Alighieri (1265-1321) and Aquinas were in agreement about one point: both Church and State were important, just in different ways, and neither should try to usurp the other's authority. Dante, however, observed first-hand the serious clashes between the papacy and empire, and tended to come down on the side of empire. If the State was a society ordained by God, then Dante saw the emperor as ruling by divine grace, and therefore no mortal should be considered to be superior to the emperor. Dante also held up the empire as the only instrument able to achieve peace.
What did the papacy think of this line of reasoning? We will see that tomorrow.