NOTES for Mar 12:13-17
The fact that the Pharisees and Herodians, who usually do not get along with each other, are ready to "join forces against" is not surprising. What is striking is the question they ask Christ. Not its content, since it is only another provocative attempt to catch Christ in His words; there had been plenty of those. What is revealing is the long, ornate introduction to the question, whose very construction exposes the deceitfulness of the questioners. Christ speaks directly about this before answering the question.
Of course, after such a rebuke one could leave the question unanswered. But even this situation Christ uses to give people the opportunity to look at things more sharply than usual. In answering, He brought into the world the understanding that the incomparability of the Highest authority and earthly authority does not mean the denial of earthly duties. But Christ's answer is also a call not to fall into voluntary slavery to yet another idol, while remaining free and faithful to God.
The short phrase about God and Caesar overturned humanity's ideas...