NOTES for Mat 22:19-21
The Pharisees' question and Christ's answer about the tax to Caesar reveal an enormous difference in initial assumptions. Trying to catch 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 knows examples when national dignity demands resistance, while the Lord through the mouth of a prophet calls for submission to the conqueror, for he is the instrument of the Lord.
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 precisely this case they called the Herodians with them, in order immediately to hand the Lord over to those very 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 one another within the framework of the proposed alternative, even if it is deceitful. For them the Kingdom of God is a politically successful earthly Israelite state that the expected Messiah will head.
But the Lord's answer leaves not one stone standing from this assumption of the Pharisees. The Kingdom of God and Caesar's kingdom appear in Christ's answer as two nonintersecting 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 swarm of infusoria in a yard puddle cannot be a comparable likeness of the earth's biosphere. Thus Christ's answer completely rejects the Roman, and also later Jewish, sacralization of the earthly kingdom. Later the apostle Paul will give final explanations on this topic 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 render God's things to God. Even the question of the relationship between the earthly and heavenly kingdoms recedes into the background. The main thing is not how you arrange your earthly affairs and relationships; the main thing is how you build relationships with God. Whether to pay tax to Caesar is not such a simple and obvious question, but it is solvable. Human life, however, is determined not by this, but by what one brings to God.