People who believe in Jesus and dedicate their lives to worshiping Jesus and following Jesus are called to be in the world. A select few, the smallest minority, are called to the isolation of life in a monastery where most of life is spent in solitude, praying alone. I think that call is as legitimately issued by God as any calling. Perhaps the call out of the world at large and into the inner world of constant solitary prayer went out to Anna, the daughter of Phanuel (Luke 2:36-38). However, most Christians are not called out of the world permanently. Most of us are called by God to serve Him in the world as witnesses who tell the story of salvation in Jesus Christ.
However, we are not the be of the world. The grime of sin and the desperation of those lost and far from God should not rub off on believers. Rather we should affect unbelievers with the grace of God so that whether or not they turn to Christ after having met us, their lives are brightened because they experienced God's love having received if from us. The world should be a holier place because of the presence of Jesus' disciples. We disciples should not be tainted or dirtied because we've been in the world. We're here as God's emissaries. Heaven is our home and our time here should not lead us to become more worldly.
The "in but not of" discussion pertains to all areas of life. In our relationships, in our moral conduct in social environments and work environments, in casual comings and goings, and in every conceivable human interaction, Christians either live as those sent by God, or we live like those who do not know God. The "in but not of" dynamic permeates every corner of life including the arenas of money and power.
These issues are in play in a specific exchange Jesus had with men who approached under the guise of innocent seekers. Their humble approach could not hide the devious purposes in their hearts. They were spies from the scribes and chief priests and they came with a question intended to trap him in his own words (Luke 20:20-26). "Teacher ... is it lawful for us to pay taxes to emperor or not?" By lawful, they meant lawful in the eyes of God. In 6AD Judas the Galilean led a revolt against Roman occupation of the land God had promised to his chosen people, Israel. Part of Judas' platform was the notion that it was a violation of God's law to pay taxes because the taxes were engraved with an image of Caesar. Such a "graven image" violated the 2nd commandment (Exodus 20:4).
Of course the catch to this type of zealous religious commitment was that if an Israelite refused to use Roman coins and pay the tax, he would be breaking Roman law. The Romans had all the military power as their crosses of crucifixion showed. Judas the Galilean went to his death for the sake of Israelite independence (that never came). The scribes' spies in Luke 20 did not have such valor in their hearts. They wouldn't die for a cause, but they were happy to either lead Jesus to do so or to expose him as a charlatan. They were engaging in political game playing only for Jesus the consequences were potentially fatal. And the scribes - Israel's religious leaders - did not care.
In answering these insidious inquirers in Luke 20, Jesus could say, "Yes, pay the tax." In this way, he'd appear to be deferring to Rome's might. He'd lose his groundswell of support and be seen as a paper tiger who cow towed to the unclean gentiles.
Or, Jesus could say, "No, don't pay it." He'd look heroic, but word would quickly be leaked to the governor and Jesus, who was already raising eyebrows, would be seen as dangerous, subversive. In that case, his arrest would be a forgone conclusion. Jesus wasn't looking to get arrested. He never avoided or sought it. He spoke the truth about man's sin, God's love, and the community of faith he was building. He spoke that truth openly even as the highest temple officials in Jerusalem opposed him. And, maintaining his composure even before the torturers whip, he spoke that same truth after he was arrested.
Maybe that's the key for us - 21st century Christians trying to live as witnesses in the world, but as people who are not of the world. Maybe the quickest way for to point to Jesus is to speak and to live the truth (lovingly and compassionately) no matter what it may cost us.
To the questioners Jesus asked, "Whose head and title" is on the coin? The acknowledged that it was the emperor's image, and so he told them to "give to the emperor things that are the emperor's and to God the things that are God's" (v.25). To understand Jesus' response to this tricky inquisition, we must remember Luke's point of view. He and his readers knew Jesus was Lord, and God was god of everything. So, as powerful as he seemed to human eyes, the emperor himself was in actuality subject to God. He along with every other person belonged to God.
Jesus was not about to be painted into a corner by a coin. The most important part of his answer is the part about giving to God what belongs to God. To those spies sent by the chief priests, Jesus issued a challenge. What exactly belongs to God? Everything! So, they needed to stop trying to pick Jesus apart with disingenuous queries. They needed to step back and realize that they themselves belonged to God. They needed to give what belonged to God to God. They needed to submit their own hearts to God's glory and to God's purposes. Until they did that, they were not ready to ask Jesus questions. Until they recognized God as the ultimate and only true authority, they were nothing more than puppets manipulated by the religious leaders who sent them.
Luke's worldview, which was Jesus' worldview, was that God was and is in charge of everything. God allows humans to sin and we do. God allows the consequences of sin to play out in human society. This accounts for most of the messes we have to deal with. However, as corrupt and vile as the world can sometimes seem, God is always God and is always in control. Jesus demonstrated this by reducing the ridiculous test, do we pay Caesar's tax or do we not pay it, by establishing a timeless truth. "Render to God the things that are Gods." They knew as do we that all things are God's. And as followers of Jesus, we must speak that truth in all places and times, no matter what may happen as a result of our saying.