One day, as Jesus was teaching the people in the temple and preaching the gospel, the chief priests and the scribes with the elders came up and said to him, "Is it lawful for us to give tribute to Caesar, or not?"
But he perceived their craftiness, and said to them, "Show me a denarius. Whose likeness and inscription does it have?"
They said, "Caesar's."
He said to them, "Then render to Caesar the things that are Caesar's, and to God the things that are God's."
And they were not able in the presence of the people to catch him in what he said, but marveling at his answer they became silent.
D. A. Carson, Christ and Culture Revisited, p. 57:
When Jesus asks the question, "whose image is this? And whose inscription?" biblically informed people will remember that all human beings have been made in the image and likeness of God (Genesis 1:26).
Moreover, his people have the "inscription" of God's law written on them (cf. Exodus 13:9; Proverbs 7:3; Isaiah 44:5; Jeremiah 31:33).
If we give back to God what has his image on it, we must all give ourselves to him.
Far from privatizing God's claim, that is, the claim of religion, Jesus' famous utterance means that God always trumps Caesar. We may be obligated to pay taxes to Cesar, but we owe everything, our very being, to God. [Quoting David T. Ball:] "Whatever civil obligations Jesus followers might have, they must be understood within the context of their responsibilities to God, for their duty to God to claims their whole selves."