Within the home, the difference between Christians and non-Christians is not the use of the things of this world (food, shelter, etc), but rather "the respective purposes to which they put them."
The same is true of the city:
The earthly city which does not live by faith seeks only an earthly peace, and limits the goal of its peace, of its harmony of authority and obedience among its citizens, to the voluntary and collective attainment of objectives necessary to mortal existence.The City of God--at least that part of it "on pilgrimage in mortal life"--uses this peace not as an end in itself, but in anticipation of the time when earthly peace will no longer be necessary. As a result, the City of God can never be more than that of a "captive and an alien" due to the cross-purposes for which we use the same things as the city of man. Nevertheless, the City of God "has no hesitation about keeping in step with the civil law which governs matters pertaining to our existence here below." When it comes to the necessities of human existence, there is no reason we can't work together.
But! "Now comes the difficulty." In looking at these necessities of human life, worldly wisdom concludes that there must be a multiplicity of gods to be worshiped and that creation must determine the creator, while the City of God knows that there is but one God and that He alone is to be worshiped. So while we share material goods and goals, this does not mean that we share a "common religious legislation," and so we have "had no choice but to dissent on this score and so to become a nuisance to those who think otherwise." And so we have "had to feel the weight of their anger, hatred, and violence, save in those instances when, by sheer numbers and God's help, which never fails, she has been able to scare off her opponents."
This City of God, however, is no closed fortress.
She invites citizens from all nations and all tongues, and unites them into a single pilgrim band. She takes no issue with diversity of customs, laws, and traditions whereby human peace is sought and maintained. Instead of nullifying or tearing down, she preserves and appropriates whatever in the diversities of divers races is aimed at one and the same objective of human peace, provided only that they do not stand in the way of the faith and worship of the one supreme and true God.So we work together with the city of man so long as we can, even as we subordinate those goals to the hope of heaven. Only there will we have perpetual peace and eternal life, which we have now by faith but will have then in communal reality.
We reject skepticism as "insanity", even as we admit our own limitations and inabilities to know the fullness of truth because of our flesh and sin. To help us through our limitations, we have faith and Scripture which guide and shape our lives and give us enough despite our doubts and ignorance.
"The City of God does not care in the least what kind of dress or social manners a man of faith affects, so long as these involve no offense against the divine law. For it is faith and not fashions that brings us to God."
So, even philosophers don't have to give up their philosopher's clothing when they become Christians, so long as they give up "their erroneous teachings." Likewise, we don't really care whether you live a life of action, contemplation, or a mixed life, since faith and stretch through each of these. Both leisure and action can be used for Godly ends by a Christian. Leisure should be used in pursuit of truth; action for good works. The example of the latter is the office of bishop, who is supposed to work rather than bask in the dignified glow of office. "Thus, no man can be a good bishop if he loves his title but not his task."
Leisure likewise is to be used correctly, i.e. in pursuit of wisdom--unless this becomes a distraction from our duty to love others, at which point we need to put the books away and get to work.