NOTES for Mat 22:19-21
The Pharisees' question and Christ's answer about the tax to Caesar reveal a vast difference in their initial assumptions. Trying to trap the Lord, the Pharisees ask a question about priorities: what is more important, obedience to an alien but actually powerful authority, or national self-determination. It is important to note that both of these supposed values lie outside the religious sphere. Moreover, by that time Israel's history already knew examples when national dignity demanded resistance, while the Lord, through the mouth of the prophet, called people to submit to a conqueror, for he was the Lord's instrument.
Further, the Pharisees expect that the Savior, proceeding from the idea that the Kingdom, that is, the sole rule of God, is above all, will say that one should not obey earthly authorities. For exactly this case they brought the Herodians with them, so that they could immediately hand the Lord over to those same authorities. But the whole point is that the Pharisees suppose that the Kingdom of God and the principate of Augustus are phenomena comparable in nature and scale, that they can be related to each other within the framework of the proposed, though deceitful, alternative. For them the Kingdom of God is a politically successful earthly Israelite state headed by the expected Messiah.
But the Lord's answer leaves not one stone upon another of this assumption of the Pharisees. The Kingdom of God and the kingdom of Caesar appear in Christ's answer as two non-intersecting planes, incomparable with one another in scale. The Kingdom of God belongs to eternity and embraces all that exists, while an earthly kingdom, limited in time and space, cannot even be its small likeness, just as a crowd of infusoria in a yard puddle cannot be a comparable likeness of Earth's biosphere. Thus Christ's answer completely rejects the Roman, and also later Jewish, sacralization of earthly kingdom. Later the apostle Paul will give final clarifications on this theme when he says that our citizenship is in heaven, and that we should obey earthly authorities only because, and to the extent that, they oppose evil and violence.
But the most important thing in Christ's words is the call to give God's things to God. Even the question of the relation between earthly and heavenly kingdoms moves into the background. The main thing is not how you arrange your earthly affairs and relationships; the main thing is how you build your relationship with God. Whether to pay tax to Caesar is not such a simple and obvious question, but it can be resolved. A person's life, however, is determined not by that, but by what he brings to God.