In Mark 12:13-17, Jesus is put to the test by the Pharisees and Herodians by these questions: "Is it lawful to pay taxes to the emperor, or not? Should we pay them, or should we not?" Jesus then takes a denarius (one day's wage-- the sum of money one gets for giving his body to work for a whole day) and asks, "Whose head is this, and whose title?" Jesus then says, "Give to the emperor the things that are the emperor's, and to God the things that are God's."
This text often gets quoted in our modern day by Christians wishing to make a case for obedience to the government. However, such an interpretation is to miss the larger point of what Christ was teaching. Jesus uses a particualr type of Aristotlian argument and rhetoric here-- everyone in that day knew that whatever bears the image of someoe belongs to that one. Knowing his audience, Jesus also knew that the people believed themselves to be made in the image of God. What Jesus does with his words is deliver a stinging critique on our lives... although we are made in the image of God, we are giving ourselves daily in the work of Caesar. For that daily work to the empire, Caesar gives us his coin for a day's wage. If we are giving ourselves to Caesar in the first place, then why not give him his money back.
Jesus subversively is telling the crowd, why do you work for Caesar and his empire? Why do you work for his economy? Why are you participating in the world of Caesar?
In other passages, Jesus helps the people imagine a different world wehre everyone has their own vineyards and where everyone is invited to the banquet table and where everyone is given the same day's wage for their service to God. The parables are these new imaginations and dreams for the future. Jesus imagines an alternative world with an alternative vision for economy, commondity, and community.
If we work for the empire and recieve its wages, then we must pay its taxes. But Jesus is asking, "Why are you working for Caesar in the first place? You bear the image of God, not Caesar's!"