Mark 12:16

And they brought it. And he saith unto them, Whose is this image and superscription? And they said unto him, Caesar's.

Cranfield wrote that:

The legend (on the coin), which is abbreviated, reads (in full) "Tiberius Caesar Divi Augusti Filius Augustus Pontilex Maximum." Both legend and images set forth the mythology of the Imperial cult and so troubled the consciences of religious Jews.[9]

Jesus at once took up their admission of carrying and using the coins bearing Caesar's image and superscription; and the coinage of ancient rulers was held to be theirs, even though in the possession of the people. The astounding implication of this is that since the money was already Caesar's, there could certainly be no harm in giving it back to him! Such an answer had to be inspired. The mechanics of Christ's answer regards the difference in the word "give," as used by the Pharisees in "Shall we give?" and the word "render" as used by Christ in "Render unto Caesar." The latter word means "to give back" (to Caesar the property that was already his); and all of the Pharisees on earth could not have found anything wrong with a reply like that.

As usual, however, the Lord did not stop with merely confounding his enemies; he went much further and showed that Caesar's dues, legal as they were, must be viewed as limited, and subordinate to the higher obligation owed to God himself. See next verse.