Thus far in this chapter we have looked at some of the conflicts Jesus had over his authority and some of the conflicts he had over differing values. In this final section, I want to look at the way Jesus engaged the secular authorities of his day, especially the Romans. Jesus really didn't get into conflict with the powers of the "state" until the end of his earthly mission, but he had some things to say along the way.
One of Jesus' most famous sayings on this topic comes in Mark 12, when some individuals are trying to trick Jesus. They ask Jesus "Is it right to pay the imperial tax to Caesar or not?" (12:14). If Jesus says "no," they can perhaps get him in trouble with the Romans. If Jesus says "yes," then perhaps they can get him in trouble with those who think he is the messiah, the king of the Jews.
Jesus' asks to see a coin and gives his well-known response, "Give back to Caesar what is Caesar's and to God what is God's" (12:17). The saying drives a strong wedge between matters of God and matters of the secular government, as if they are two distinct kingdoms that have nothing to do with each other. Unsurprisingly, different Christian groups have seen in this response slightly different models for how Christians should engage the culture around them. 
Some have taken Jesus to imply a kind of isolationist position, as if Christians should not get involved in broader culture or politics. The Amish would be an extreme example of this approach, but there are Christians who refuse to vote or engage political issues today. Some Christians have traditionally been "conscientious objectors" who do not participate in the wars of a country. Those things are the realm of Caesar and a Christian should stay out of them.
The Lutheran tradition has generally taken a different tact. Jesus seems to say to pay the tax. In a fascinating story in Matthew 17:24-27, Jesus indicates that they should not have to pay the temple tax. But so that they will not cause trouble, he has him go fishing. In the mouth of the fish he catches is a four drachma coin, with which Peter pays the tax for himself and Jesus.
So the Lutheran tradition has usually taken the approach that we are in these two kingdoms at the same time. They have nothing to do with each other, and they are in conflict with each other. It is impossible to reconcile the two to each other. So our lives are full of contradictions. The lives we live in the secular world don't fit with the lives we live in the spiritual realm.
Both of the above approaches seem extreme. If we look a little more closely at what Jesus might have meant, there is first the matter of coinage and money. The world of Galilee was primarily an agrarian world and a world of trade. In our world today, we cannot escape using money. But in Jesus' world, money might easily be seen more as a foreign element, the stuff of taxes and foreign powers. The coin with Caesar's face on it has nothing to do with God. Give it back to Caesar.
The words of John 19:11 to Pilate capture the situation well: "You would have no power over me if it were not given to you from above." In the background of Jesus' conformist approach was surely the belief that God was going to come and judge the Romans in due time. As Paul would later put it, "What business is it of mine to judge those outside the church? ... God will judge those outside" (1 Cor. 5:12-13). 
So the ethic Jesus taught in relation to secular authorities was an "interim ethic," not in the sense of an ethic only for while he was on earth but only for the time before Jesus returned...
 The classic here is H. Richard Niebuhr's Christ and Culture. There have been a number of responses in recent days, including D. A. Carson and others***
 Interestingly, Paul goes on in 1 Corinthians 6:2-3 to indicate that, when Christ returns, we will take part in the judgment of the world. It's just not a function he saw Christians performing in the meantime.