[20] And they watched him, and sent forth spies, which should feign themselves just men, that they might take hold of his words, that so they might deliver him unto the power and authority of the governor. [21] And they asked him, saying, Master, we know that thou sayest and teachest rightly, neither acceptest thou the person of any, but teachest the way of God truly: [22] Is it lawful for us to give tribute unto Caesar, or no? [23] But he perceived their craftiness, and said unto them, Why tempt ye me? [24] Shew me a penny. Whose image and superscription hath it? They answered and said, Caesar's. [25] And he said unto them, Render therefore unto Caesar the things which be Caesar's, and unto God the things which be God's. [26] And they could not take hold of his words before the people: and they marvelled at his answer, and held their peace.

In this acted parable, Jesus is showing us that religious powers will send their agents into the midst of those who are doing the will of God, and those agents will pretend to be honest men, but their purpose will be to try and find something that can be used to bring those doing the will of God before the civil authority.
These agents will admit outwardly to the things being taught, that it is truth. Then they will attempt to get those doing God’s will to say something against the civil government, such as questioning whether they should pay taxes to the government. Those doing God’s will should answer that there should be a separation between the religious power and the civil power and that we should render to God the things that are God’s and render to the government the things that belong to the government. This answer will prevent the agents from being able to deliver those doing God’s will as lawbreakers to the government.