What does Mark 12:15 mean?

Local religious leaders are attempting to trap Jesus by asking Him a controversial question: should Jews pay taxes demanded of them by their Roman conquerors (Mark 12:13–14). The "trap" comes in the dangers of a simple yes-or-no answer. "Yes" would anger the Jewish people, and "no" would make Jesus a rebel against Rome. As usual, Jesus defeats the trick question by exposing the real issues involved. He does this, in part, by using the Roman coin used to pay those taxes as a visual aid.

When this tax was first established, in AD 6, a Galilean named Judas responded by leading a rebellion. He believed that the Jews had only one master, God, and to pay the tax was to spiritually and morally subjugate oneself to Rome. Jesus does not accept Judas' conclusion, but many did. In AD 66, the pressure in the nationalistic Zealot's sect will reach a boiling point. They lead a revolt which the Romans meet in AD 70 with the destruction of Jerusalem.

The problem with Judas and the Zealots' belief is that they put the cart before the horse. They know that God will give Israel peace and sovereignty if they obey Him (Deuteronomy 28). Instead of obeying Him and waiting for God to fulfill His promise, they try to take the blessing by force.

In God's dealings with Israel, foreign rule is always seen as unfortunate, but it's not treated as something the Jews need to or can escape from. It's typically a judgment for disobedience (Jeremiah 25:8–14). In the church age, there are no theocracies for God to judge, but every believer is subject to civil authorities that are either secular or influenced by a religion other than Christianity. There is no Christian nation, and there's not supposed to be. Those that claimed to be in the past did so because the power of the church served to enforce the rule of the king, not of God.

When the southern kingdom of Judah disobeyed God and God judged them by sending them into captivity in Babylon, Jeremiah admonished the people to submit peacefully (Jeremiah 27). We are called to do the same. We should influence the government as much as we are allowed, and if a civil law overtly contradicts God's command, we are called to obey God—and suffer the consequences (Romans 13:1–7; 1 Peter 2:13–17). But despite what the Zealots believe and the Pharisees hope, God never promises the Jews they can win sovereignty without His direct involvement. And He never promises Christians freedom from immoral secular rule.