What does Mark 12:17 mean?
Devout Jews hate that they are ruled by Rome. They hate that even their part-Jewish kings and tetrarchs rule with Rome's authority. They yearn for the fulfillment of the covenants God gave Abraham and David, that they will have their own nation, ruled by David's descendant. The trick question posed to Jesus was whether Jews "ought to" pay taxes to the Romans. The assumption is that Jesus will either give a simple "no," making Him a rebel against Rome, or a simple "yes," angering His Jewish followers.Jesus' answer here does more than prove the trick question is misleading (Mark 12:13–14). It implies something crucial about our obligations to God. Coins bearing the image of Caesar are rightfully owed to Caesar—so to whom do lives bearing the image of the Creator belong (Genesis 1:27)?
Jesus isn't explicit, here, about what the Pharisees and Herodians are withholding from God. He does go into more detail on the behavior of the Pharisees and Scribes in Matthew 23:1–36. Their public worship is designed to win the admiration of the people, not actually worship God. They burden the people with false traditions that draw them away from true God-worship. They value the minutia of the Mosaic law more than the just, merciful, and faithful character of God's heart (Mark 7:1–13).
Cultural angst aside, there are many advantages to living in the Roman Empire. Despite periodic rebellions by the Israelites themselves, this region is relatively safe. Pax Romana means the Jews don't have to worry about being invaded by Assyria or Babylon or Egypt. Trade routes are well-established, and thanks to geography, Israel is in the middle of the land-route between Europe and Africa. The Empire has a common language and a common currency, making trade convenient. Rome and its Caesars are the reason for this. The coin required to pay the tax has a graven image of Emperor Tiberius and wording that identifies his parents as deities. If the Jewish religious leaders have no problem carrying and using such coins to the temple itself, they should have no problem returning the coins to Caesar.
Considering all the ways the Pharisees neglect the true worship of God, paying an earthly tax to an earthly emperor shouldn't be an issue. Jesus' answer defeats the attempted trap, and further establishes Jesus as a philosopher to be reckoned with. Eventually, His critics will realize this and stop trying to trip Him up (Mark 12:34).