This brief story points out exactly how the world treats Jesus, and exactly how Jesus treats the world.
Note, to start with, that the religious leaders understand (v. 18) that Jesus has publicly called them out by telling the previous parable. He has named them as unfaithful tenants in God's vineyard. Their response? They could have repented, but instead they sent spies hoping to catch Jesus in words they could later use to convict him. Note also that they have increased the stakes in the game: They're no longer just trying to smear Jesus in the court of public opinion, but their question is specifically about how to deal with the Romans. They want to get Jesus not just disgraced, but executed.
The heart of their question: Is it lawful for us to give tribute to Caesar, or not? The people hated their Roman overlords, and popular sentiment would immediately answer, who cares if it's lawful -- we need to rebel! The Jewish leaders who sent these spies, however, were colluding with the Romans to maintain a relatively stable political climate so they could maintain their power base.
Jesus takes his answer, again, to a new level. It's not just a question of taxation, he says, but of identity. Show me the coin. Whose image is on the coin? (Jewish coinage, by the way, never included a human form like Roman coins did, because of the Old Testament prohibition against graven images.) Caesar's image is on the coin, they said. So Jesus, knowing that these spies as well as everyone else in earshot will get the allusion, says they should give to Caesar the things that bear his image (i.e., the coins -- pay your taxes) and to God the things that bear his image.
No listener would have missed this: In Genesis 1, God said he was going to make human beings in his own image and according to his likeness. So even in the face of this seemingly niggling question about taxation, Jesus points to the ultimate authority of God and challenges his hearers toward repentance: You are made in the image of God. Therefore, pay your coins to Caesar but give yourself to God. Stop worrying about self-preservation and render your heart to God, then see where he leads you.
It is not very hard to transpose Jesus' comments into our own era. We who tend to be so consumed with the matters of costs and benefits, of ownership and acquisition: Whose image do we bear? And are we giving ourselves, heart and soul, to God, living as his reflections, his image, in this world?